Clefable and Wigglytuff were decent in gyms because they either slow down Machamp or force a switch. They’re not necessarily good at defending, they just take up time.
Hariyama will still be okay, it just loses some bulk.
Houndoom will still be decent. If you don’t have a full team of psychic counters or like variation then it’s usable.
Slaking is and has always been trash. Send it to the grinder. Its only usefulness is making gyms tower and deterring casuals from attacking.
Jynx will still be a decent counter if you need an ice attacker. If you don’t have a full team of Mamoswine when it’s released or Articuno, you might want Jynx. Or again if you like variation.
Omastar without legacy moves is underwhelming.
Donphan is decent. It can double as a budget Tyranitar counter with Counter and Earthquake. On defense it has Play Rough which hurts Machamp.
And most importantly, upgrade your Pokémon storage. 600 is not enough. I’m at 1000 and even that’s not enough. I have 70~ set aside for distance trades for my friends (I’m well over the gold medal for distance trades), as well as tons of dratini, ralts, larvitar, beldum, etc waiting to trade for bonus candy (or transfer if the Halloween candy event is better).