Hmm sttike strike bash prone then back off (they can OA at disad if they want) moving your move back and they have to spend half their move to get up and so cannot retaliate is intriguing - or as some would say worthless even if your other allies can daisy chain in for advantaged strikes.The useage of shield master you liked was cheese, though, and SS isn’t.
Cheese doesn’t mean “it’s powerful”, it means that something is being used in a way that bends RAI to go beyond what it was meant to do.
Shield Master is still a good feat. 5ft of forced movement as a bonus is good. It can often put enemies into positions that they can’t escape from without getting rekt, or just give you allies better room to maneuver, make the target unable to OA an ally, break a grapple, etc
Knocking them down is still useful to your allies, and getting back up still costs half their movement, which makes it useful for locking down an enemy that wants past you. And the only way initiative can make it useless is if the enemy goes after you but before any of your allies go. That isn’t exactly going to happen all the time.
As for the defensive stuff, they should be relevant quite often. You’ve basically got evasion as part of a feat. If it isn’t coming up often for you...sorry your DM isn’t using dex save spells?
Regardless, this doesn’t ruin the feat, it literally just clarified what the rules mean, and discourages cheese.
Yup.