This way still depopulates pretty well.  I did't catch the transport in time but I had 22.5 with about a 43% resistance so I wasn't overly worried.  But 2.5 invaders won with conventional warfare.  I expected with an almost 4 to 1 advantage I would retain the planet while I sent more ships to protect that area even if I lost most of my population.  The colony ended up with I think 3.8.  I see that as a lot of depopulation and that there isn't much need for other types of invasion.  

I can see why invasions would in the initial testing phase kill 10 times the number of invaders but now that there are other options and its time for balance.  I don't mind conventional warfare to favor the invader against 2 to 4 times the number of defenders but beyond that it should be because the invaders are much more skilled.