The reason I like Crusher, in addition to being a half-feat, is that on a successful hit (and I do indeed intend to punch people when they're held), I can relocate an enemy by a single space. It might not seem like much, but with no saving throw against it, it can be a powerful tool against stubborn creatures. It essentially turns every melee attack into a shove attack as well. Perhaps not the strongest tool, as part of a strictly grapple-based loadout, but certainly useful.

I'm not really feeling Bard, especially because this character's purpose is to frontline the fight, holding down troublesome monsters for the DPR teammates to unload upon. I'd very much like to stick to the peak martial classes... probably a progression like starting as a Fighter, branching to Barbarian at 2, then 4 levels of fighter to get Battlemaster, the ASI and Extra Attack. Similarly, while Rogue is an interesting thought for that Expertise, Prodigy/Skill Expert takes care of that, in the one skill we need most.

I'm really not feeling Tavern Brawler. I'd trade away half of an ASI for, essentially, the ability to conditionally grapple as a bonus action. Since Unarmed Fighting is almost certainly already part of my build, the d4 strikes are irrelevant, and if I have powerful fists, I don't really care about using barstools, treasure chests, giant rocks, or kobolds as weapons.

That said, Skill Expert does seem like a better choice than Prodigy, and while I'm not super thrilled at playing a custom lineage, it does have its advantages (especially in getting STR to a ridiculous level at the very start of their career). Right now, it seems like the ideal level progression would be lv1 fighter, lv2 barbarian, then lv 3-6 fighter to get Battlemaster, the ASI, and Extra Attack. From there, either push Fighter hard to get tons of feats (Grappler, Mobile, Athlete, Mage Slayer, etc), or splash more Barbarian, possibly to unlock the Bear Totem super-resistance.

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A related question about grappling prone characters... doesn't that mean they're pretty much stuck on the ground, while you get all the benefits? Grappled means speed 0, and speed 0 means they can't stand up unless the grapple is broken... does that mean I can continue to unload on them, while they flail around on the ground in frustration?