Jefe Bergenstein
Legend
Probably should have phrased it differently, but that's the bulk of what a warlock gets over another 9 level caster. There's a reason its mainly a 2 level dip class.If you want a warlock that is only "powerful" in terms of at-will damage, and even then only as good as a fighter with a heavy crossbow and no further class features, sure. You still need to add damage to all those attacks by spending a resource in order to surpass other at-will dpr classes. Doing good weapon damage plus ability modifier is...not especially impressive. You are basically 1 feat (crossbow expert) ahead of a ranged fighter. Cool. Compare DPR with a dex battlemaster with a longbow, and I bet the warlock loses, without requiring the fighter take a feat.
Meanwhile, our bard in the OP has fairly low AC as a non-dex primary light armor character with no shield, and idk even know where to begin addressing the idea that the bard is a strong full caster. Magical Secrets is good, sure, but it's still a known spells caster whose list is really only strong in control, which only "wins the game" in white rooms populated by spreadsheets. (don't get me wrong, I love a spreadsheet, but they don't give you all the necessary data to determine game balance)
It's a fun build, but it ain't breaking the game.
I've played a version of this character in someone else's game (well, lore, not swords) and felt it's OP compared to most anything else I've seen.