How do People Feel About Stadium WITHOUT Rentals? It's Way More Difficult to me

I know most people like to play Stadium with Rentals Only. Hear me out though.

I think it'd be fun and unique to be playing through Red/Blue, but after every Gym Battle, you swap over to the corresponding Gym Leader Castle fight on Stadium. For instance, the past couple days I trained up a party of 3 (had a bunch of self-imposed restrictions) which ended up being a Squirtle w/Bubble, Pikachu w/ThunderShock, and Butterfree w/Confusion.

Obviously, I steamrolled through Brock in Red with just Squirtle, however when I swap to Pokemon Stadium; it's a completely different story.

I attempted to make it to Brock probably about 10 times before even getting to him, where I got swept by his Omanyte because my Squirtle could barely touch it with Bubble and Pikachu got one-shotted by SURF. The pokemon you face in Stadium have insane moves and are EV trained, while my little guys were fresh from Route 1 and Viridian Forest with 0 TMs.

I understand as my team grows and I get TMs it might get easier to where it's similar to using Rentals. But the sheer fact that I can throw on a Starmie with Bubblebeam, Thunder, and Minimize and solo Brock with it in Stadium, including all of the Gym Trainers except for the one with Bulbasaur where I can swap to a Jynx with Psychic and Ice Punch, is so much easier it's not even funny.

At this point, I'm starting to think it's actually impossible to defeat Brock from Gym Leader Castle after beating him in Red, with the same party of 3.

Yes, I am scaling up all of my party to level 50 before fighting him. I just feel like there's literally nothing I can do about the omanyte so if he brings it, I'm done. Leading up to Brock, there's a Butterfree with Psychic, Razor Wind, and Mega Drain which is crazy good. There's a Sandshrew with Earthquake and Strength, and a Dugtrio with FISSURE that seems to land way too often.

In my other attempts, I've used Beedrill, Nidoran male, and Bulbasaur mixed with the pool of 3 I mentioned earlier. If anyone has any thoughts or tips, I'd greatly appreciate it.