Honestly, at this point the mod offers you so many options that its incredibly hard for the player to be pidgeonholed into using one strat only, and thats a good thing. There's a great degree of availiable in regards to soldier types, weapon options, research branching, mission options, base facility options, craft options. The fact that choosing some things push some options away while bringing some unique or semi-unique things your way also spices this up a fair bit, me thinks.
So yea, TL;DR, game is winnable through multiple different strats as long as you prepare properly, keep the research going and dont bite more than you can chew. Really, the only thing that players really need to do in every run to not be rolled over by the game is to keep research going at a decent rate, since its not exactly easy to take down mercs using only boarding guns, and even then I think a clever/determined enough player could pull through with enough patience and luck.
Came back to this only recently, gonna prob do another run, one which mostly ignores psi related stuff since that requires a whole lot of effort to be even usable and even then its only actualy useful once you have the right tech to apply it with.