Both Repelling Blast and Battle Master's Pushing Attack are chosen abilities though, you pick them at the cost of other abilities.
Battle Master even has to use a resource to push.
Yes Repelling Blast is "free" but warlocks pay for this by having a very small pool of spells, and less spell slots. Eldrich Blast is meant to become very powerful.
I enjoy shove as a bonus action, but I see that it's a bit of an overpowered ability as it stands.
If it was bade an attack action, and you could use it as one of your attacks with multi attack (as you can in 5e) then I think it would still do it's job.
Battle Master might have to make a choice and spend a resource but considering how many battles have powerful shoving spots it's not exactly a hard choice and they were already going to spend that resource on some form of damage steroid anyway. As for Warlock, sure it comes at the price of being a Warlock but it's not like your blasts are bad. Eldritch Blast+Hex is far from bad damage and, like with Battle Master, ranged shoving in and of itself is incredibly strong to the point that you hardly need any other spells besides Hex and Misty Step to be effective.
