So what if you can't have a "perfect" build for everything without umbral formas? Just use them on the stuff you like the most and be done with it.
You can get through 99% of the games content with no rivens, no archon shards, and no umbral mods on your gear with no significant issues. I just got back into the game after being gone for a long time and am blazing through the newer stuff and the things "tuned for full squads" solo.
Treat umbral formas as an award for some piece of gear. Don't just throw it on because someone tells you to, put it on because you enjoy it enough that you will continue to use it for a long time to come. I missed a lot of umbral formas and I saw qorvex and tried them for a while, liked them so much I spent one of my few umbrals I had left over on him. He worked perfectly fine before, but I just enjoyed them so much they basically deserved it imo. I didn't use it because they needed it, I used it because I liked them so much that I wanted them to be that much better.