It's still a bit of a balancing act, since neither fighter nor rogue gives you anything that can grant you advantage on strength checks (except for a level 13 swashbuckling rogue using Xanathar's guide, but that's a bit "out there"...), which is either necessary or merely extremely useful depending on your particular school of thought.
Then there's the fight between Shield Master and Tavern Brawler... SM can grab-shove an opponent using only one attack action (+bonus action), but then there's not a whole lot you can do with that one person you have grappled unless you also have A: Monk levels (in which case you shouldn't be using a shield), B: Tavern Brawler (for its least synergistic effect) or C: Spellcasting (either to prebuff with a +damage effect such as Hex or Divine Favor, or a Verbal-only/shield-is-a-focus attack spell to be used on the grappled opponent).
TB, meanwhile, allows you to swap the actions around a bit (bonus action for grapple, attack action for shove), but only if you have at least one level of Extra Attack, but it does give some minor damage options to use. It can even technically be used with nothing in your hands for double-grapple utility.
Unfortunately, it requires you to
first land a successful attack in order to kick off the grapple. You could work around this by leading with the shove for advantage against a prone opponent (oppronenent?), but if the attack-grapple doesn't land after that then you've basically only succeeded in making them spend a few feet of movement next turn to stand up.
There's also the extremely strange philosophical discussion as to where the line between "improvised weapon" and "weapon" should be drawn, and how generous your DM feels about whatever random junk you happen to have picked up and swung about...
Additionally, the archetype is generally even more reliant on extra attacks than other brawlers, due to trying to get the most out of grappling and shoving... There are fast ways of getting a "poor man's" version, such as with the aforementioned Shield Master or Open Hand Monk, but those come with their own troubles. Otherwise, you're looking at a fairly significant investment in fighter levels, for the additional Action Surge and all its nonsense, or some other class that provides Extra Attack... Which means your character doesn't really blossom until you're several levels in.
Bards actually get a bunch of goodies related to grappling. Valor Bards gain bonus proficiency with medium armor and shields, expertise, spellcasting (including Enhance Ability for STR advantage so long as you can manage to maintain the concentration), as well as getting Extra Attack at level 6, all in the scope of one class. But they deal with d8 hit dice (suboptimal, considering), as well as again having to wait until CLevel 6 to really get moving. Also they don't have heavy armor proficiency, which would help bump ever-important AC up a touch and alleviate some of the MAD-ness.
But, I mean, bards seem to do most things better than other people in 5e anyways...
Do prions count as disease? Hoof and mouth disease?
I'd imagine they should... Inasmuch as they're actually modeled...
Then again, a pedantic GM could have Purify Food and Drink also sterilize away all their gut microbiota on the grounds that they're a disease by virtue of getting other people sick.
...and therein lies the rub. Hence the firm rooting of this question inside the "philosophical" realm, due to the subjective definitions of "food" and "disease". Or even "poison" for that matter... Cast Purify Food and Drink inside a candy shop, and all the chocolate disappears because it's toxic for dogs/gnolls.