There isn't a clear "grunt" frigate, and part of that is the fault of the rocks-paper-scissors game balance we have.  No matter what unit you pick as the workhorse, there is a hard counter to it, so if you rely heavily on them you're going to get countered. 

Just to be clear, are you advocating spamming as the most viable strategy?

**edit**

Looking at the rock/paper/scissors balance thing, I think you could work a mid-late "cap ship killer" vessel.  Something conceptually like a bullet proof vest with big gun sticking out the front of it and nothing but jello for protection in the rear.  Something you bring in after the enemy is engaged that rushes up through the fray and puts all of its juice on the cap ship.  Ball parking stats: 10-15 supply, 1200-1600 credits, 1500 m, ? c, hull 1800 front / 400 rear, shield 1200 front / 100 rear, 20-25 dps in one weapon, range 1500, speed 1200-1500, acceleration 150-175.  Maybe a ramming special ability, but otherwise nada.  If I knew jack about modding I'd try that out for you.

first, no, im not advocating spamming, personally, i think its stupid for reasons i wont go into now

second, i was comparing voyager based on crew and ship size... seriously, its deceptive, but those light frigates arent exactly small... neither is voyager... but she isnt as big as a Star Trek Federation Galaxy or Soverign class starship either, id compare those with Cielo or even Kodiak Cruisers... but then again, look at all the tech and firepower the Soverign class has, vs the Kodiaks 3 autocannons...

yes i know its a game... and it requires balance and a certain amount of slack to be effective as a game.... to be honest, i dont know quite what im looking for... guess im just sick and tired of the typical one unit-one role cliche, where tanks are purely anti-tank, despite the fact that most if not all tanks have some sort of anti-personnel weapon mounted. here the LRF and LF could easily be put together... or the LF could recieve a missile attack and the LRF a closer range autocannon attack, but i can already tell you that the huge majority, if not everyone on this forum, will not like this idea.

i guess i wanted a different ship, one more like a capital ship, but smaller and less powerful, maybe with some abilities, but not necessarily. something with multiple banks and multiple weapon types, just to come into a battle, unleash hell, and make everyone think, oh damn!

i agree that all the combat roles are covered, like i said though, some more variety, i mean, at the moment, we have 2 support cruisers, a carrier, a flying missile silo, and what is supposed to be a bad ass cruiser... i guess what im looking for is the proverbial battleship, bristling with weapons, able to take it and dish it out, and able to compliment other ships or simple duke it out one on one, the LF does not cover this role, like you said, its role changes to become (again) a support ship.... everyone is supporting, who is fighting? maybe if you gave HC's 3 banks or so, and maybe a missile or equivalent attack, id be happier, as it is, combat in Sins nowadays is kinda boring imo

LFs range in crew complement from 75-150.  Roughly the equivalent of Archer's Enterprise to Voyager (though Voyager may be a bit bigger) or the smaller of the two USCG cutters.

Cap Battleships range from 2500-9000 (but Vasari live in their ships).  Enterprise D was between 1000 and 1100, which I don't think would last long compared to Sins caps.  A Nimitz is ~5200 including the air wing and maintenance. 

The smaller frigates are overcrewed and the caps are undercrewed.  But then it's kind of doubly arbitrary since the crew complement has exactly zip to do with the production and operation of these vessels.

**Numbers taken from the printed Training Manual that came with the retail boxed game.

when im comparing scales for objects in Sins i try to compare like to like objects, so in other words

compare ships with ships, structures with structures, planets with planets, stars with stars.

and the reason why i believe most of the frigates (light frigs, flaks, LRFs, sieges) have crews in the 3 crew-member range is because of the relatively limited capabilities of those ships. how many guys does it take to operate a ship that just has an engine system and a couple of missile launchers strapped to the sides? most of the cruisers wouldn't be much bigger, if an LRM has 30 guys maybe a Kodiak has 50 or 60. 

based on this interpretation it leads me to believe that capital ships have crews of a few hundred, rather than a few thousand. that would make them analagous to the larger destroyers or cruiser class vessels of the current U.S. Navy and not anywhere near the size and scale of the real capital ships like Super Carriers, which have multiple thousands serving on board. 

thus my earlier statement that the Super Capital ship class is just outright missing from the game. would be kinda neat to see it in an expansion pack. 

I remember Star Trek Armada 2.  The Feds get some crazy frigates like Defiant.  Its possible to overwhelmed larger ships with a fleet of Defiants. 

the spaceshuttle is very complex, (or not very complex, depending from where you look at it) compared to a navy ship. also, space is alot more hostile than the ocean, so the more people the better in space, so that each person can rely on the other. also, a space shuttle is basically used for science or supply/repair missions. now, you need two pilots (redundancy there) one person on navigation, one person on communications, one or two monitoring fuel and ship specs (an engineer of sorts) plus a couple for EVA. plu, we're only new in space, so basically, the more specialists, the fewer problems can go wrong (in theory)

now, on a cruiser, there are shifts, there is rec time, there is all sorts of bridge officers that do one thing and one thing only, instead of a one person doing a few things with the aid of a computer. there are cooks, stewards, laundry... people, engineers, military police, intelligence officers, hundreds of jobs. which is why so many people, todays military or high danger jobs like to make one person specialise so their entire attention is focussed on their one job

however, in the futre, with much more advanced computers, an intuitive UI, maybe even a direct neural interface, you dont need so many people...

i mean, the cielo has, what? 900 crew members? lets take out shifts, hospitatlity crews (i.e. chefs and cleaners and laundry) lets take out Command&Control, theres, what, weapons? one measly laser that, honestly, could be handled by a computer, during a battle i cant imagine off duty officers lazing around in the holodeck or the gym mucking around, they would be doing something... but 900 people?

i agree though that direct or classwise comparisons are difficult, because sometimes you have battleships with 100 crew because most of the running of the ship is done by a few crew members and very advanced AI

however, lets look at things logically, what does a cielo have that requires 900 crew members? what does an LF have that requires 75-120 crew members? i mean, the kodiak... what does it do? it drives up to the target, maybe uses 'afterburners' to get there quickly, then sits its ass down and opens fire... i cant see anything (other than damage control maybe) that requires more than 150 crew members... its basically a flying gun with an afterburner?