The only way to do that is to rely on guaranteed damage, much of which Pavonis has mostly removed in LW2.
This is untrue. Combat protocol is still in as the first chooseable perk for the specialist, hail of bullets for the gunner as his second rank. Grenades, have mostly been converted away from cover destruction (which I agree is much, much more OP) to a main focus of providing reliable damage, though with very well designed trade offs (making a lot of noise, destroying valuable corpses). This form of guarantees damage is so important that Legend players swear by it. I doubt they'd be able to compete the campaign without them. Hence, it is a critical part of the XCOM formula. Do you sacrifice valuable corpses for guaranteed damage? Do you sacrifice a pretty cool perk for guaranteed damage? And it is a good thing, if the answer isn't always yes.
To allow the player a strategy that minimises the chance of failure to the point that it is effectively eliminated means you lose the feeling of being in a real battle. You lose the tension and uncertainty, a campaign with both lows and highs and the stories that emerge out of those moments.
This I agree with. BUT it doesn't mean that giving the player control over certain aspects of the game so that they retain a sense of urgency is a bad thing. Look at Hearthstone. By all accounts, it is an RNG clusterfuck but that is part of its charm to a certain group of players. It still is able to retain interest in a segment of players that hate RNG, because it still retains many aspects of predictability that reward player skill. If that was removed, do you think there would still be a vibrant competitive scene for it?
It's not a good analogy to compare XCOM to Chess. A better analogy is to compare it to poker, and people are screwed by RNG in poker all the time -- more than in XCOM! -- and yet people still play and love the game.
That is an interesting comparison you just made. Because, from what I believe, XCOM has much, much more similarities with chess than Poker. It is a tactical game with tactical simulations. Chess is precisely that, with absolutely 0 RNG to precisely elevate the importance of player skill. In XCOM, you move your pawns about the board hoping to 'outwit' the enemy AI. You don't draw cards from a deck and play with the hand that you're drawn. The latter is only a consequence to a clusterfuck of RNG thrown to the player, designed precisely by the game designer.
So I guess in the end you and I enjoy playing different games. I want my XCOM to be a tactical simulation that rewards player skill. Sure, it is fun if it is hard. But I don't find it fun if it is hard because of the computer incidentally rolling good dice against me. I am glad that LW2 gives room for player failure. But any "player failure" that happens should precisely only happen BECAUSE of player failure, and NOT because of RNG mechanics out of the player's control, that makes the player feel bad. I want the game to be hard because of overwhelming, avoidable and outsmartable odds, NOT because of mechanics introduced that are unfair to the player. That is the kind of difficulty that is rewarding and fulfilling to conquer.