I've been fiddling with if thr Baldur's Gate 3 version is balanced: it's basically advantage on weapon damage dice, it doesn't have the 1/round limit. But it's hard to say really, since the other Origin feats don't boost damage (unless you count shillelagh or true strike from the magic adept feats). It's just that Savage Attacker doesn't "feel" good, regardless of if it's actually balanced.
Shillelagh turns a club from a 1d4 weapon to a 1d8 weapon. Savage Attacker let's you roll 1 weapon damage roll with advantage. 1d4 to 1d8 is +2 damage, which is comparable to duelist. 1d12 to 1d12 with advantage is 6.5 to 8.5. So, maybe it is balanced? But shillelagh is only part of the feat, half or one quarter depending on what you value more (personally, 1 1st level spell 1/day doesn't seem valuable to me, but people rank the magic adept feats high). Shillelagh also scales with level and with extra attack, while Savage Attacker doesn't.
Last, I think part of the "feels bad, man" feeling of Savage Attacker is knowing that once you get extra attack, you aren't going to be able to choose which damage roll to reroll because it's not a reroll. You could roll twice on your first attack and get 2 8s, then roll a 1 on your second attack.
If it was something simple like crit on a 19, it might feel better, even though that might also be weak.
