I discussed this over a few 1v1 matches with blackmagic and am on the same page. The returns for rushing for an offworld are greater than the costs that may be incurred doing so, including interest payments. The strongest colonies are those that can can produce the required resources to build the offworld fastest.
Expansive, Scavenger specials.. (High triangle carbon/high alum close together), Robotic. Whichever has the quickest path to the offworld based on the map.
Part of the reason for the offworld necessity is that the returns are high. Typically, there is a resource that sells for ~600-700 offworld. This allows, when combined with adrenaline rush, to really increase your cash quickly. Adding slowdown strikes to be immune to goon squads will help... but only a little bit since both players will get their offworlds hit. Resource prices on world just don't compete with the returns from the off-world at the end of the game.
Holograms and goon squads. It is very easy to protect an offworld market from blackmarket effects. With a 60 second black market delay, and a 60 second "defended" period granted by the goon squad, the player with the offworld is ALWAYS protected, and the returns easily offset the measly 10-15k that the goonsquad will cost to replace since a launch will occur before that happens. You can't even pre-buy a BM effect to burn off the goonsquad to hit the offworld. Oh, and you get the sabotage right back at your own offworld. Even though holograms "don't work well" its still a free protection against someone not paying attention to their opponent.
Game duration. Even if you wanted to, the game is not long enough to support running up the black market prices to the point where it becomes a meaningful decision to protect the offworld or not. It's also difficult to raise the cash necessary to do so, provided the game could be extended. Artificially extending the game via slowdown strikes, EMP, and power surges isn't enough for this reason. A smart player won't leave themselves open to huge delays. a 1v1 game isn't long enough in duration to allow longer term investments such as patents or engineering bay to start to pay off. Level 5 and the offworld come too soon and can't really be delayed with good play.
Stock prices. In earlier versions, stock prices and resource prices enabled you to make a mid game push to buy the other player. It's not currently practical to do so as you can't raise the cash mid-game to make a meaningful attempt to buy out the other player. Once a player defends themselves, the combination of stock prices bonuses (shares purchased bonus, and bought share buyout multiplier) makes it not possible to complete the buyout. Whether the amount spent buying stock at that point is worth the investment is undetermined.
With the way things are right now, after around the mid game, the game feels like its just being played out to finish. The winner is determined as the leader can protect him/herself indefinitely, and has the cash/black market access to impede the player who is behind. It takes a combination of great play/bad play to overcome a deficit. I forgot who made the post a couple of months ago on this topic, but I definitely see it currently in 1v1. Undermining the leader is very difficult.