Not exactly.
There’s a factor that both E4 and Gyms possess(more so the Gyms) that maintain their value. Not the difficulty, but rather the cooldown time.
Because no matter how long or short of a time it takes for someone to beat them, the cooldown time stays the same.
Main example, Person A could sweep Gym rematches with, say, Kyogre, and Person B could stall/use 5+ Max Revives/Potions and take longer.
Either ways, after they beat the Gym, they still both have to wait 18 hours to battle the Gym again. And there’s no item or Pokemon that can speed up this process.
E4 is the exact same way.
So the point I’m trying to make is that the E4 doesn’t have to be on impossible mode all the time to have value. It all lies on cooldown time.
If people were suggesting a method to shorten cooldown times, I’d agree that there would be problems, but the fact of the matter is that they’re not.