Personally I don't see how less RNG-y boarding mechanics would "ruin" the game experience, especially if you balance the boarding correctly. Consider the cost of a new ship, let's say a 45,000 credit destroyer. Now let's say the player is given the option to board said ship instead of buying it. So long as the repair cost plus the marine cost are balanced to be similar, the progression will stay largely the same.
Heck, allow the boarding success rate to be controlled by how many marines are committed, with success being guaranteed with enough personnel. Just have the casualty rates guaranteed as well (with a +/-10% margin for FUN!) and you have a generally balanced mechanic that allows players to have agency, let's them still get lucky (committing to boarding with less than the required marines and just hoping to get roll big), and is still has cost that can be measured in credits. Granted, it doesn't address which ships are available for boarding, but at least it deals with the boarding mechanic itself.
Obviously the boarding skills would require a rework with this, but I think it would be more fun than the current mechanic of "Pray to RNGesus".