>>55335474Because you're going in with perfect knowledge. The game wasn't made for turbo autists to minmax the fuck out of everything. It was made for 10 year old jRPG players in the 90s.
You have to go into the E4, with a team that's ready for anything, because you don't know what they're going to have. So you should have good coverage for anything. Aside from Brock, the game was always sure to give you coverage options, before each gym battle. They even invented a Pokemon that you degenerate want to have sex with, to give the player even more coverage options, just to be sure that the player wouldn't be prevented from advancing, with Eevee.
Each of the gyms are supposed to showcase 1 type and E4 members are supposed to showcase 2 types.
If you're sweeping the E4, you've either minmaxed with your perfect information, captured the 3 Legendary birds, or you grinded a lot of extra battles. The first two weren't balanced around, and there's little they could do to stop you from grinding, as that's player choice. If you just fight the trainers and the given random encounters, you'll still be at least 10 levels below the E4(likely more if you have a full team). Doubly so, if you consider the fact that Game Freak assumed that you'd be rotating Pokemon in and out of your team on the regular.
Considering that R/G released in early 1996, I'd say they did a great job with it. You have no perspective.