You guys haven't thought about this the proper way... Like I said in another thread, I wished they made a crossover between Pokémon and Digimon... And that would require giving a 4th stage evo for some pokémon at least...
There is one key difference between digimon and pokémon when comparing the strength of both:
Most fully evolved pokémon represent the adulthood of that species... That would be the equivalent of the Adult/Champion level of Digimon... However, the levels in Digimon are (not counting babies):
Child/Rookie
Adult/Champion
Perfect/Ultimate
Ultimate/Mega
So, that's 4 stages... Pokémon can only get to the third but just like I said, the strength and characteristics of fully evolved pokémon is more similar to the Adult level than the Perfect level, and the Adult level is the 2nd stage of Digimon... This happens because while Digimon go from child to adult, Pokémon families with 3 stages can be seen more like:
first stage - child
2nd stage - teen
3rd stage - adult
There are exceptions to this and those exceptions are basically the new evos of older fully evolved pokémon from Gen IV. The best examples I can give are Rhydon, Electabuzz and Magmar. They all look and have the strength of an adult level, yet GF gave them evos. And those evos are the best equivalents of Perfect level digimon...
Think Greymon for example:
Greymon evolves into MetalGreymon. What are the changes? About half of its body is metallized (the flesh, which can be seen in its tail), its right arm becomes a mechanical arm, its grows some sort of wings on its back, its helmet is covered with metal and its chest gets some sort of missil launcher... But it is quite similar to its earlier stage, more than Greymon and Agumon...
Now think Rhydon and Rhyperior... Rhydon evolves with the Protector item... Rhyperior is little more than a Rhydon with a reinforced Rock armor, it now has a big rock at the end of its tail, it gains an additional horn and its arms can launch rocks... The change is not as big as the change from Rhyhorn to Rhydon in terms of design and adaptations...
Now, since some pokémon already have 3 stages, we can't simply erase the 2nd stage (the teen), and reduce the strength of the fully evolved...
So, while I was doing of project of my own, I thought about this possibility to equate the strength of pokémon and digimon:
first stage pokémon -> digimon child level
2nd stage pokémon -> digimon adult level
3rd stage pokémon -> digimon perfect level
This of course depends on the strength of pokémon...
Pokémon with BST until around 360 would match the child level,
Pokémon with BST from ~360 to ~480 would match the champion level,
Pokémon with BST from ~480 to ~560 would match the Perfect level.
And that's where the 4th stage comes in... The 4th stage of a pokémon would match the strength of Ultimate/Mega level, meaning Pokémon with more than ~560 in its BST would match the Megas...
So, pokémon like Dragonite (and the other pseudo-legendaries) would not be the ones to get a 4th stage... They are already strong enough... Only pokémon with around 535 (I said 560 but that's only for the strongest mons, 535 is the average) or less would be candidates to a 4th stage... And their evos would have around 600 BST, maybe a bit more so that there would be significant changes in the stats (probably maximum 610)...
Mascot legendaries would still be the strongest pokémon and can be compared to digimon like Omnimon and stuff like that...