I need a better Pokemon team for Sapphire Version.

You may want to consider actually training the Sableye. It has no weakness, so it can take hits all right, if it's closely leveled to what it is facing.

Which May battle is it that you're having trouble with? That'd help some, because I'd know what areas you have access to, or can get to, for Poke'mon recommendations.

 

Lotad is an exceptional Poke'mon. It's uniquely typed as a Water/Grass, and can take hits okay, especially when it evolves into Lombre. The only type of moves it need to fear is Flying, Poison, and Bug, but the last two are rarely used, while the first is uncommon.

You can find a Lotad on Route 102. It will evolve into a Lombre at level 14. To reach it's third form, Ludicolo, you will need a Water Stone. But I wouldn't use one until it reaches level 45, at which point it learns Hydro Pump.

You can also find a Ralts on Route 102, but it evolves at level 20. It's definitely worth the investment, though it is difficult to find, being a rare encounter.

 

Little concerned that you've got two water types on the same team but you're early enough in the game that it's gonna be hard finding a huge range of Pokemon to make up for that. Still, I'd try and explore other avenues for building the team. Swampert's an excellent starter so would keep Marshtomp. Wingull? Eh. But gotta admit. Kind of a bitch finding a good offensive flying type especially so early in the game.

Highly recommend Ralts but I find until evolution, Ralts' stats aren't anything to sneeze at even in a little cup setting.

Sableye might not be a Pokemon I'd keep late in the game but he's a decent Pokemon at this point. Level him up. I find dark types are great for screwing with the opposing team.

Geodude's a great choice, especially as a wall. Not super experienced with using them in battle but he'll come in handy.

But, if you find you need a good offensive Pokemon, than Aron's your guy. Steel and rock, has a hell of a good attack and defense. I'd only consider using Aron on the team if you don't care for Geodude. (I'm pretty stringent about types, if you didn't notice).

This being May, you'll want to pay attention to the Pokemon she's using and try and make sure your team covers as many bases as possible. And this is basically how I go about in any Pokemon game- I try to make sure my teams cover as many possible type match-ups as possible. Having two or more Pokemon of the same type, I find, often opens up the team to a critical disadvantage.

Another recommendation- Shroomish. Yeah, yeah. He looks stupid. But Shroomish will evolve into Breeloom. Duel fighting/grass type. That does, however, leave him open for a critical double flying weakness. But if you need something that packs a punch, Shroomish/Breeloom's worth looking into.

And another type. Train your team so they're all close in level. It's natural that as you slog through gyms, you'll probably have one member at an advantage because they have a type advantage or they've got an offensive advantage. It's tempting to rely solely on one Pokemon but in the face of battle, having only one Pokemon close in level to your opponent can be a huge disadvantage should that Pokemon faint and you're left with a team of Pokemon much weaker than your favorite.

So to repeat: try and diversify the team and level them up.

Hope that helped.

 

I was going to suggest Shroomish as well, but Breloom's main thing is knowing Spore, a 100% accuracy sleep move. Problem is, you have to not let Shroomish evolve until level 45, which overlooks a lot of Breloom's moves.

If you need a good decoy, Shroomish is worth considering. But you'll have to be patient.

 

You could train a Slakoth to level 18 to evolve into Vigoroth, which is an okay Pokemon. Vigoroth evolves into Slaking. Despite having the ability Truant, making it skip a turn after making a move, Slaking is still useful due to its high attack and decent speed.

 

Ditch Wingull and Geodude.
Raise up Sableye.
Catch Aron and Shroomish/Lotad and level them up too.

Since I'm guessing Grovyle is a problem for you, Zubat might not be such a bad shout either. (Plus Crobat is good. )