I don't see what's so bad about Bards, Sorcerers, and Warlocks being able to change a single spell once per day. Clerics and Druids already can choose all of their spells from their entire class list daily, at no cost. Wizards can pick from their spellbook every day. I can only see this versatility leading to more fun.
It shoehorns pretty hard into the whole Wizard shtick of being the king of Versatility, especially since it applies as a feature to Cantrips as well which they kick wizards the scraps of changing upon level up.
if any class should be able to change cantrips on a Long Rest, I think it should be Wizards. I would expand the Bard/Sorcerer/Warlock ability to swap out spells they already get on a level up to just apply to their cantrips with this new "spell versatility" and then call it good.
The Primal Beast still uses the Ranger's Companion features rules, right? So does it still take the "Add your proficiency bonus to the beast’s AC, attack rolls, and damage rolls, as well as to any saving throws and skills it is proficient in." Part? It obviously replaces how hit points work. If it doesn't take stuff from the existing feature, then there's also no explanation for how to control it. It's a little unclear what we take from the existing feature and add to the new one.
Everything from the existing feature still works exactly as is.
The only difference is specifically the Primal Beasts themselves. It has its specific stat block baked into the class feature, which is something they're leaning pretty hard (see Wildfire Druid).
That's it. It just gives two new "animals" options to make companions and just gives the stats so you don't have to go chasing them.
There is literally
no changes to the Beast Master features at all besides giving two new companion options.
That + the Revivify spell for keeping around non-Primal Beast companions, but that is from expanded spell list, not the Beast Master option itself.
Everything else that boost the companions is specific to these two companions. The extra HD to heal on short rests, the extra hit points, the Primal Rebirth option to raise your companion to life, etc are all baked into the companion, not the Subclass.