I really don't get why some people are saying that the middle stage starters don't match with the leaked final stages.
- Dartrix is starting to develop the "hood", even if it looks just like a leafy tuft atm, it's even more focused on launching quill-like feathers (it can even change their trajectories), it starts to show more its open wings and the seed-like brown feathers are almost identical to the final leaked stage. To confirm that even more, it has "dart" in its name, and it could be inferred that "Rowlet" is partially derived from "arrow". Even as a minor touches, its bowtie starts to point downward as the hood laces on the final form, and its tail as now 2 lobes instead of 1 (in progression it would only make sense for the last one to have 3, as it is indeed in the leaked one). This middle stage is actually even more related to its supposed last stage than other previous starters.
- Torracat is getting much bulkier, but mostly in its forearms, which are used to deliver strong punches. Its beard/mane and tail are now getting much more similar to that of the leaked last stage, and the red pattern on its forehead now touches the eyes, exactly like in the last stage. The most obvious connection though it's clearly the "fire sac": even if Torracat has it on its neck, it's exactly what the last stage has on its "belt", and an extruding front-facing fire sack wasn't obvious at all from Litten's design. This one has the weakest inference of the three, but still pointing towards the leaked stage more than other previous middle stage starters, so it's still pretty solid.
- Brionne is obviously getting more "feminine", something not deducible from Popplio. Its collar becomes a multi-layer dress, layers that the leaked last stage still has (as a collar, as a "skirt", on its tail and an additional one on its "hair"). Its tail is getting more fish-like (sea lions don't have a fish-like tail at all, mermaids do as our leaked final stage), and it now has two small braids formed by pearl-like spheres (popplio doesn't have "hair" at all, last leaked stage has fluent hair with pearl-like spheres in it). Brionne is also getting whiter and the 2nd stage has plenty of white (while Popplio not much), and it's white in every part Brionne is too (tail, fins, snout, "pearls"). Its concept is shifting from a clown to a ballerina/idol that is far closer to the singer/diva 3rd stage. With a bit of speculation, it's stated that Brionne behaviour is related to the moonlight, pointing towards a fairy type, highly likely considering the Selkie/Mermaid theme of the last stage (psychic type is a second possibility, but it's more related to space objects rather than the creature influenced by them, as we see with Lunaala not being a fairy type AND Solgaleo not being a fire type -nor Lunatone or Solrock respectively- while Clefable indeed is a fairy along with moves like moonlight or moonblast). Brionne is a perfect match with the leaked evo as much as Dartrix, but even more undoubtable considering that it was even less deducible from its first stage.
What I'm trying to say is: there's no doubt the leaked starters final evos are legit (with Mallow confirming it months ago), but the middle stages mostly confirm that their also close to the final designs. That wasn't sure months ago, they could've been dropped official ideas, but now it's different. I'm not saying they will be identical of course, we don't know how old those sketches are, but I'm pretty sure the design will be pretty much that, and I wouldn't be surprised if it didn't change at all. People who're saying that they're "too big of a jump" from their respective middle stages just didn't analize the designs well enough. If you're still hoping for a quadrupedal final Litten's evo, well, there's still a possibility that the 3d model will have a different stance from the sketches, something like Mega Abomasnow wouldn't be too farfetched, but I actually doubt it as it would hamper the "wrestler concept" (likely an homage to Tiger Mask, Gamefreak isn't new to homages to classic franchisings).