You're missing the point that the addition of the rivens is to have an *evergreen* reward, something that always has a potential value to a player. Pathos Clamps have a very *limited* use, totaling at most 1460 used just to get one of everything (unlocking drifter weapons, applying incarnons to *every possible variant*, building kullervo twice and rauta once). If you use plat to unlock the drifter weapons and only want to apply incarnons to one weapon variant out of every type, that drops down to 620, and will drop even further if you purchase Kullervo & Rauta once, or even if you decide to buy Kullervo twice. So eventually the need for lots of pathos clamps will run out. Now, the Duvirir vendor already has evergreen rewards for pathos clamps for those that like doing the Duviri open world content, in the form of being able to buy exilus adapters, arcane adapters, forma blueprints, potatoes, kuva, and a riven mod.
Meanwhile, Circuit currently *doesnt* have an evergreen reward, hence the addition of 2 riven mod choices in addition to the incarnon genesis adapters.
also, there's been no indication Duviri is meant to be some "soulframe alpha test". You can dislike it all you want, but dismissing it as something it isn't just devalues your entire statement.
Veiled rivens have been uncapped for months now, if not a year. They start counting against cap when you slot them into a weapon to generate the challenge and unveil them. Until that point, you can have as many as you want.