Please sell me on why I'd want to ever play a bard, when they seem so weak...

[sophontteks]

At actually grappling opponents they indeed compete very well with barbarians. At staying alive after restricting an enemy to close range (the “secret” requirement for any grappler), they fall decidedly behind barbarians (and even grappler rogues thanks to their uncanny dodge and evasion, or grappler wizards thanks to arcane ward+shield).

At mobility (a nice boost for grapplers but not strictly necessary) they again fall behind the barbarian and rogue thanks to increased movement speed and cunning actions, but are about on par with the wizard.

At the end of the day, if I want a grappler, there are at least three other classes I’d choose first now that the prodigy feat makes expertise available to all.

Don't forget bards have the level 1 spell, longstrider, for +10 movement. And the grapple trip combo gives the enemy disadvantage on attacks. It's not the grappled target which is the problem, it's other targets nearby. With a high AC a bard can more or less take a target out of the fight by grappling. Beating their AC with disadvantage is pretty tough.

But mostly grappling isn't an all or nothing strategy. The valor bard pays very little for excellent grappling. I definately agree that a barbarian is better due to just being a better martial class, but the Bard is a full caster on top of it.

A barbarian may be looking to grapple targets by charging right into the thick of it. A valor bard is instead using their spellcasting primarily. But when enemies inevitabley push past the tanks, the bard can pin them down in a single turn with a high success rate and no slots used.

This changes over time. When valor bards get magical secrets they could pick up enlarge/reduce if they wanted to be more dedicated grapplers. At which point they have a pretty sizable advantage over martial grapplers.