Escaping is similar to disengage abilities like his knockback. He doesn't get as close to his turret with it, but it still puts a gap between him and an enemy.
Plus plenty of fighters do have legit escapes
and if they build pure damage, they are in effect assassins
Also tank builds on assassins are basically dead and gone. Riot has tweaked the worst offenders so much that they are just worse than real tanks. Which is a good thing, but just doesn't agree with your point. Tank ekko and fizz have been terrible ever since the reduction/removal of their flat %missing hp damage, and lower base damage / higher ap ratio tweaks