The same goes to Harsh Mentor, this card in diverse metagame is not good. Against some decks you need 4, against many you'd rather see anything else than a 2/2 that occasionally hits an opponent for 2 (fetchland usually).
I think you're right that Harsh Mentor gets worse the more diverse the meta. OTOH, in a meta full of Ravagers and Ballistae, Harsh Mentor can really shine. Every time a player sacs an artifact to pump Ravager, every time a counter is removed from a Ballista to ping someone or something, every time a counter gets added to a Hangarback Walker, every time a Factory gets animated (or pumped), is a good opportunity for a Mentor to do 2 damage to that player. A single Harsh Mentor can severely disrupt a Ravager deck and multiples can be totally deadly.
On the gripping hand, Oath decks, Landstill decks, Two-Card Monte, PO decks, and just about everything else is not going to tremble in fear at a 2/2 that has little to no effect on them. If there were ever a time for maindeck Harsh Mentor to shine, the current prevalence of Ravagers should be it. (But it probably isn't.) Sideboard may be different. If this deck wants Mentors at all, think more about sideboard.
My 2 cents.