The torrenting app will just consume all the extra space, leaving just as little for gaming as there was before.
totally untrue. fq_codel manages normal torrents just fine in the presence of gamer-style traffic. We tested against torrents in fixing bufferbloat a lot! Pure aqm systems like pie (in docsis 3.1) do pretty well also. cake (per host fq) can make even insane amounts of torrenting (or slashdotting!) bearable.
The key issue here is contention, or a busy egress interface - that's when buffering occurs. I do not understand why adding capacity, or reducing the probability of a busy egress interface, "won't help at all".