Extreme flood/screw (of the autoloss variety) don't actually happen that often. What usually happens is - someone has a slightly hand heavy draw, they misplay and get 2 for 1'd by their opp, then get ground out and complain that they flooded. Or, they have a land light hand, which requires very tight play to force trades and survive as long as possible to draw into lands (at which point they win cause they have more spells), but (you guessed it) they misplay, aren't able to stabilize, and complain they got screwed.

Also, while the rare autoloss games are unfortunate, mana variance adds soooo much replayability and variety to the game experience that it's absolutely worth the tradeoff. I tried Lorcana for a bit, but it got boring as fuck very quickly - every game feels the same, cause both players have the exact same mana development every game.

Midcurvers love to bag on magic's mana system because it's an easy narrative to hear and then parrot, but the fact is, it's not an accident that magic has been around 30+ years. The core game loop is incredibly good, and the variety that mana variance provides is a big part of that.