Though Aang had mastered all 4 elements at the end of the series, in my opinion, he is still not a better waterbender than Katara, a better fire than Zuko and a better earth than Toph. What do u people think?

That makes sense. Even though he can fully utilize all four elements, that does not make him a master in any of them. The only one he is a master of is Airbending, hence the tattoos.

Their master of Waterbending is Katara, their master of Earth Toph, and Fire Zuko.

In that way, he is still strong, but it does not make all his companions useless.

Aang by himself was able to manipulate all four elements, but he was new to each, except airbending, and therefore was not as good as his friends; in the Avatar state, he is no longer "by himself" but has connected with all the past Avatars, and n this state is more powerful than any one bender.

Toph will always be the best earthbender and I think azula was the best firebender but Aang and Katara are quite equal now