If the villains do have lots of ways to break your stuff, it can be a good idea to play out a load of cards, just to get yourself a buffer of cards you don't mind getting destroyed while you put out the cards you actually want to keep. Depends on how often stuff-destruction occurs, of course, in relation to the rate at which you're putting out cards that can be destroyed...
That really depends on the villain, though.
Citizen Dawn and Omnitron both destroy *all* Equipment and *all* Ongoings, so putting out a buffer isn't an option with them. Later expansions, obviously, drift away from that sort of in-game punishment, destroying cards only based on (H).
Yeah, I was speaking generally rather than specifically - pretty much everything in Sentinels is dependent on the current situation in terms of which decks are being used, which cards are out, etc.
I wish it were three or four copies.
Most of the heroes in the game are fairly worthless without a good bit of setup (the Sentinels is one of the handful of exceptions). Fighting some of the hardest villains (challenge Cosmotron, ultimate Dawn, some VOTM layouts) in the app has gotten me used to the drastic limitation of the Play 1, Power 1, Draw 1 setup. Most heroes just don’t get very much done with only one card played or one power used. Once you get three or so cards combined, you are able to actually start achieving something.