Should Critical Hits deal x2 damage in 5E D&D?
The champion needs more.
In such a game, the Battle Master actually compares even MORE favorably against the Champion. At least with feats, the Champion can get the Great Weapon Master's bonus-action attack on crit more often than the BM, which closes the gap between the two somewhat.(PS: No, I don't allow Feats or Multiclassing... probably one reason why Champions are so popular for Fighter choices in my game).
Ugh, no. The confirmation roll as implemented in 3E slowed down gameplay and was often a total buzzkill. "I rolled a nat 20...! Oh, wait, I didn't confirm. Boring old normal hit." Your rule of giving players something on the first 20 even if they don't confirm is an improvement, but it still seems like you're gating the excitement unnecessarily.In my games I like the old 3E rules of confirming a Critical Hit, which I carried into my 5e games. First 20 (or 18-20 for Champions) is an auto hit and deals max damage. Then they get a roll to confirm the critical with a second d20 roll. If they hit the AC (or get an 18-19 For the Champion) it's double max damage. If they get a second natural 20, it's instant death.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.