Spiderman isn't stuck at the same powerlevel. He has even became Captain Universe. Symbiote suit, spidey armour, iron spider suit..etc change his power levels as well. Not mention that time he grew two more pairs of arms or the time he mutated fully into a giant spider. He also upgrades his webbing and adapts to his opponent to make it feel like he is progressing. Just like other comics characters like batman.
But, you are right. Getting stuck isn't all that bad. If there are other avenues to explore.
But, getting stuck like ash ketchum would be not cool while others in your own universe improve would not be cool.