At 20th level you get 4 attacks with a bonus attack if you use 2-weapon fighting. If you action surge that's 9 attacks in 1 turn, each with a 5% chance of a fumble.
As far as confirmation rolls, yes that is a way to mitigate the impact and is something I did try for a while myself. Ultimately I just found that it wasn't worth the overhead and it just slowed down the game. It still didn't really solve some of the issues either, primarily that a lot of casters don't ever do an attack roll and that a "fumble" for the archer types is really a penalty to the people engaging the enemy directly. The former there was no answer, the latter we made the archer re-roll to see if they hit. But it was still that poor schmuck fighter in melee that took the brunt of the damage.
If your group has fun with it, it doesn't matter if I think it's one of the dumbest common house rules out there. I
might consider it with the confirmation roll, but I'd probably want to play a caster that never rolled an attack.