I found this funny. In the same sentence you as for races to be more distinct, and the bashed a race that has a distinction.
And in that same sentence I also requested "broad mechanical viability" which clashes with being heavily slanted for a particular role. The half-orc could likewise keep much of its distinction (damage dealer/berserker) simply by adding a few rules for how their features can also apply to spells while also expanding the number of character archetypes it supports.
I agree with this, but it is really hard to do and achieve the mechanical viability you mentioned earlier and to not make trap races. The want them to be "balanced" so I don't think they will go to wild.
Personally, I redesign all races because I don't care about trap races. My players are not out to find the best combo of race, class, feat, etc. So I don't need to worry about every race being roughly on par. Our current group is: 2 elves, 1 halfling, 1 lizard folk, 1 dragonborn (who can transform into a Large dragon), and one Large Yuan-ti. I have also had a player be giant and another be a unicorn.
I bet they get some odd stares when they roll into a new town. On topic, I don't even think that it's impossible to balance large PCs, but we haven't even seen them attempt it. The playtesting feature of Unearthed Arcana seems criminally underused since they never put up anything really 'out there'.
That is not true. They clarified that these were tested and considered balanced for general play. The note was about how to play those races, not mechanical viability. Doesn't mean they are well designed races, but your statement is wrong.
At least the ones in Volo's come with a blurb that says "Some of these races are unusual in that they have a reduction to an ability score, and some are more or less powerful than the typical D&D races-additional reasons for the monstrous races to be used in a campaign with care." (page 118) So even as far back as the release as Volo's, we've seen that they're willing to to go back to old paradigms when they feel like it (score penalties) and also willing to put out options that are out of line with their established narrow framework (+/- power). Yet even the way they break their own rules is boring! If they're willing to put out yuan-ti for potential play, with innate spellcasting, immunity to possibly the most common damage type in the game, and magic resistance, the least they can do is try to put out some alternate rules for running tiny/large humanoids, or other off-beat options.