Byakuya doesn't scale to big Gerard (that scales to shikai Byakuya) to any extent btw.
Bankai Byakuya can't even harm Gerard, big man slaps his petals away. It ain't shit to him.
Toshiro and Byakuya carefully plan out what they're gonna do, which is Toshiro freezing him, then Byakuya hits him with every sword of his 2x AP attack once he's frozen (via what they planned, except for the strongest attack part, that was byakuya's addition to it)
Then, Toshiro uses his freezing which is stated by him in the fight to function as a form of power null and weaken shit, and then Byakuya cracks FROZEN GERARD, as literally his whole body is frozen and no blood is ever spattered when that's done. Via the manga, no, even with the strongest attack Byakuya doesn't scale to Kenpachi nor Gerard.
Gerard could be > base Aizen (not saying he is btw, just as a hypothetical) with byakuya being as strong as he is and it'd go the same (if toshiro would freeze him just the same