My advice is to not expect too much when it comes to the feature of the game known as rivens.
I and many others complain on the first day of nerfs or whatever just to voice our dissatisfaction when the nerfs felt unnecessary and say what should have been done or changed about the riven system in general as well as how they should or should not judge how a weapon should be nerfed
We will realize the complaining is pointless because:
De is a business and regardless of what the ideal setup for this part of the game is, it's important to be aware that their main objective is to make money. They will setup the strategies they want to make money.
Ideally the setup that would make rivens a somewhat more bearable grind would have included these characteristics:
1500 fixed kuva reroll cost
kuva as a uncommon/rare resource drop from enemies in kuva fortress and kuva fortress enemies assisting grineer units in other tilesets (50-100 kuva per drop)
...and the list goes on.
The fact is rivens have layers of layers of rng, de nerfs them according to how they think they should whether it be for actual balance or profit related reasons, and lastly they are optional and therefore not needed. Of course, for others like myself rivens have a way to keep some players playing, but I would advise people not to expect too much from rivens because they are both a band aid fix to the real issue (being that the underused weapons are either not fun for those not using them or have low base stats) and a way for de to generate more plat sales for those willing to shell out to buy a riven from another player for their favorite weapons.
Voice your dissatisfaction when it happens if you have to and move on. Point of the game for players is to have fun and relieve stress after all 🙂
When you get them and roll them with the stats you want great, when they get nerfed, take the nerf and prove you really like the gun by keep using it.