True damage has literally no counter
Right, because champions like
that are super-easy to counter-build are the epitome of counter-play and super-fun to play against.
Wombo-combo?
I thought not.
You can out-range Vayne, CC her to shut down her auto-attacks completely, outright kill her, use her single-target sustained focus against her by forcing large-scale fights, or utilize Vayne's incredibly telegraphed play-style against her.
Most abilities can reach someone 550 range away. That's easy striking distance for otherwise pure-melees like Olaf, Mundo, and Darius with things like Axes, Cleavers, and Apprehend.
Also, the notion that defense is going to work 100% of the time promoting counter-play is kind of awkward.
1 stratagy working 100% of the time isn't about countering plays. It's just about using the same play over and over.
Which is the exact opposite of countering.
You can't always rely on being tankier.
You can't always rely on being faster.
You can't always rely on having more range.
Also - there are plenty of other game mechanics lacking a hard counter.
Tenacity and Cleanse are completely ineffective vs. suppression, knockback, grabs, knokcups, and slowing fields.
Point-click abilities cannot be out-maneuvered.
You can't do any damage to an invulnerable champion. Projectiles do not strike through projectile-blocking walls. Auto-attacks do not damage champions with 100% dodge-chance. Point-click mechanics are completely useless vs. untargetability.
Vayne's true damage is an incentive for her to navigate a play-path with a lot of counter-play avenues.