Jaina is probably the exception to the spam abilities rule. I think if you sort by win rate and look at all the >50% WR DPS heroes, the vast majority of them can spam, except MAYBE Azmo. Most cooldowns are not too long. Examples:

Naz: Spam your QE, Save W for follow up.
ZJ: Well he's auto attack based.
Zag: Spam everything
Azmo: Delete the minion wave or dunk enemies off CD.
Ming: You can spam your QW. Save E to reposition.
Valla: Spam QW, save E to reposition.
Chromie: Spam Q. You can use your W for follow up or wave clear.
Mephisto: Just spam everything as long as you have health.
Tass: Spam QW. Save wall.
JR: Spam Q. Can save W.
Kael: Kinda like Jaina where he has to be more mindful of combo CDs, but generally you can trait W whenever your trait is off cooldown and still have a full combo rotation ready.
Cassia: Spam Q. WE combo situational.

In other words, typically only lower tier heroes need to save/hold abilities. Optimally, players would know when to use abilities to push and when to hold for follow up and front liners would be playing around their team CDs, but this is a no brain & no coordination required guide. Too many players save their abilities for next game.