>>35785621Brendan, May, Sun, Moon, Hilbert, and Hilda are canonically the only protagonists with Legendaries so they’d be higher in the tier than most
However, Red has 9 years of experience under his belt, and in-canon earned the title of Battle Legend at the Battle Tree which he and Blue run.
And before anyone brings it up, yes Gold/Ethan or Kris/Lyra and Red battled, and it can be said that they were stronger than Red at that point of time, but we haven’t heard anything from them since.
Calem and Serena have mastered Mega Evolution so that puts them in a higher tier as well, since half of the protagonists don’t have that kind of boost.
In all honesty, it’s hard to decide who is the strongest out of all the protagonist.
However, undoubtedly the weakest protagonist would be
Leaf 
