I figured a mii wouldn’t look as good as a full fighter in Steve’s case since the limbs would be unfaithful to Minecraft’s style. With the mii, there’s multiple joints, and even the end of his arms would bend/turn I assume because of where the mii’s hands would be, and the elbow joint would probably be in a weird spot compared to the characters in the Dungeons trailers. A cardboard mascot costume would probably be fine, and either way I’d gladly take a costume if he wouldn’t be a fighter, but it seems like he’d either look off or be a low-budget costume as a Mii.
As a fighter, though, he’s really not limited to the animations in Minecraft, as they still imply he could move his limbs however he wants realistically (they’re also adding gestures and stuff to Bedrock Edition). New animations could be made that stick with Minecraft’s style, and he could move his legs to do a jump, his arms as well to show silly body language and other stuff even if they don’t bend at all (I think how they bend in Dungeons looks good, though, since it’s right-angles, so either that or no-bends is fine imo, but I guess I kinda prefer no-bends personally even if I still like the other). Mojang’s official trailers for Dungeons, as well as the one they did with ElementAnimation for their Village & Pillage update and the trailer with the bees, all show characters/mobs having facial animations showing personality, while still sticking with Minecraft’s blocky style instead of having rounded bends/weird model stuff like in a lot of fan animations (although ElementAnimation’s other animations and CaptainSparklez’s parodies make it look good and enjoyable imo, as they’re still largely sticking to Minecraft’s style despite some rounding in a mouth, eyebrow or elsewhere, but the pure blocky/pixel style in the Village & Pillage trailer with Villager News also looks very good and fits Minecraft more). This is why I feel he’d look better as a fighter (I imagine him moving better and stuff that way, looking good, and still fit in as much as every other character), even if I’d still take a costume and be happy he and Minecraft got some representation instead of nothing at all.
I guess, in the end, it doesn’t matter or bother me much, even if I really want him as a fighter with his own unique moveset, but I guess it does bother me how some people suggest the idea when they don’t really care/in Twitter’s case, it’s usually just someone wanting to bother Steve fans about it, which is done to Geno fans too (and bothers me then as well) but I don’t see it as often...I guess it also bothers me how some people argue Steve wouldn’t fit in but then propose the idea of just a stage or the full-body Mii costume, contradicting themselves (since they wouldn’t fit in either if Steve himself wouldn’t)...