A lot of these mons are "but why though" or "what does it even do?"

Tortle is probably the realest of this group, but it is hard to justify over Tentacool and Omanyte.

Rhyhorn is like Onix but you can't play it in the opening (and even more outclassed by Omanyte).

Marowak is a second Sandslash but doesn't have the bulk and gets revenged way easier. It also doesn't have the rolls to be worth bringing once you consider the bad matchups Sandslash + Marowak teams tend to have.

Lickitung is one of those bulky trademon leads but it also instantly loses to a burn, so why bother.

Ponyta is outclassed by Charmeleon, who is outclassed by Flareon, and all three of these Pokémon have a really unfavored and volatile Magmar matchup. I don't think Fire Spam as an archetype is that good in ZU.

Arbok stacks another mon that Sandslash farms while also doing really bad damage. Definitely a "but why though" type Pokemon.