I started in Portal/Mirage, so longer than some players have been alive 🙃.

Mana screw/flood exist on a spectrum. You can completely eliminate mana screw with decks like Lands. Others, like Oops! All Spells and Belcher, will never flood. The same is true with mulligans. Some decks mulligan really well (Dredge, Tron) while others never want to mulligan but they rarely need to (Burn). In younger formats (Standard, Pioneer), eliminating mana screw/flood or mulligans is less viable because of the smaller card pool. As you venture into older formats, those options become available.

A lot of TCGs forget they're card games and instead copy what MtG has already done. They're basically "You want to reduce your opponent's life total which is done by paying resources to play stronger cards most of which are creatures that attack." This doesn't actually eliminate mana screw/flood, it just shifts where the randomness occurs. Except now you don't have the spectrum and you've eliminated decks that prey on greedy mana bases (MUD, Death & Taxes) or ignore mana disruption (Oath, Dredge).

Eventually designers in those games figure this out. But they would have known this if they were more familiar with Magic's history and competitive scene. It's a giant red flag when they haven't played Legacy, Vintage, or Cube and are jumping into card game design from kitchen table Magic or Standard.