Keep in mind that those cover only one of 18 types. Cacturne is rather frail and slow. Does hit hard, but it often won't get the chance to (especially since most/all Water types pack Ice Beam anyways). And the next number of gyms is really bad for Grass types, so don't bother with trying to find one now.
On that note, don't expect any of the early good stuff to be good for long. Simple CalmMind Swoobat can go up to gym #8, but that's by far the best.
And if you want some good Grass types you can get early, there's Tangela after gym #2, Pumpkaboo before/after gym #3 and Petilil after gym #2. Tangrowth is a great bulky attacker that can go physical, special or both. Gourgeist is IMO the best physical wall in the game if you go back to E12 for Will-o-Wisp and Protect. Lilligant can completely sweep with Petal Dance, Quiver Dance, Sleep Powder and the right Hidden Power (ideally Rock cause it hits 4 of the things Grass is weak to. Stuff like Ice and Fire work too)(though Petilil sucks, don't use it right away).
Heliolisk is great, actually. The best Electric type in the game IMO, it's just that rain does nothing for it. It's great on it's own and REALLY good in sun. It's definitely something worth giving a shot...just not now. As said, it gets Thunderbolt at level 49 and while it does get a lot of moves via TM, you have to wait a while for them (to be specific, they're Grass Knot, Surf, Dark Pulse and Hidden Power. you'll be around level 50 when you get the first of those. you could go to E12 and breed it Grass Knot and possibly IVs for a certain Hidden Power before you get to the third gym, so that's something). But yeah, don't train it now, grind it up later when you can actually get it a decent STAB.
Yeah, like I said, none of the early things are keepers. You have bad things, things that are good for where they are and fall off soon, and things that are great later but are stuck in a currently-useless state like Petilil or Helioptile. Simple Calm Mind Swoobat can get you far, mine lasted until gym #8. A bit of a pain to get the happiness up there, but you can visit the salons, set your computer's date 1 day forward, rinse and repeat.