So I took the time to go try on the FIT 2 & 3 between the Vapor 2x Pro and the Supreme Ultrasonic & 3S PRO. I can't really get my feet into a fit 1 so didn't even bother with those.
The tongue does play into how the skate feels based on trying a FIT 3 Ultrasonic vs a FIT 3 in the 3S PRO. The Ultrasonic tongue is much better than the previous 2S PRO but it definitely does take up more space, in terms of volume compared to the more standard 3S PRO tongue. When I tried on the 32 PRO, there was less press over the top of my foot versus the Ultrasonic in the same spot due to the tongue. I could really feel the Reflex segments in the Ultrasonic.
Overall, the new supreme has more volume in the curved section of the boot or between the instep and ankle area compared to the previous Supreme and even Nexus line. There is less volume in the front half of the skate compared to the Nexus but part of that is also due to the new Toe Cap. I'd agree with the assessment that it's a slightly wider Supreme EE (Nexus D) but the heel area is definitely no where near as wide and cavernous as the Nexus. I'd call FIT 3 more like a Nexus width up front, mid section is like a supreme EE but with a little more volume, and the heel/ankle area is like a Supreme shape but the ankle and heel padding isn't like an Supreme EE (not as thick or bulky). Overall, for me, heel shape works better than the Supreme EE and Nexus as it seems like the padding is located better and shaped better for my foot.
Regarding the FIT 3 between a Vapor and Supreme, they are similar but definitely feel different. The difference is most likely due to the boot cut and overall shape. Even with the asymetrical ankles, I fail the pencil test in the FIT 3 Vapor and pass the pencil test in the FIT 3 supreme comfortably. The FIT 3 Vapor feels slightly more snug overall (at least for me) and has slightly less volume overall... is the best way I can describe it. I'm going to guess depending on the foot shape, the feel difference between FIT 3 (and the other FITs) across the two lines will be more pronounced for some and not for others.
I briefly tried on a FIT 2 Ultrasonic and that didn't really last long. The FIT 2 Ultrasonic seemed tighter compared to the previous generation Supreme D across all areas but I can't make much statement as it was an uncomfortable fit overall for me.
Side note - the Bauer fit machine put in a FIT 2 but a second scan put in a FIT 3. Using Bauer fit system - it says I have a E Right EE Left forefoot, low end instep, high volume where the foot and ankle meet, medium ankle volume, medium/medium high heel. Length was 6.5 skate size. I like my skate tight and there was no way a FIT2 would even be comfortable for me.