Honestly, the kitguns, zaws, and k-drives aren't that bad to craft, level to 30 twice (once for k-drives), and then never use again.
The real pain to getting every bit of MR in the game is the Kuva/Tenet weapons (and also paracesis/voidrig/bonewidow) needing 180 forma (2100 plat if you buy it) in total, and having to level each gun 6 times. At least most of then are usably good, though.
Also the shitty odds and ends like Railjack derelict weapons (shedu, spectra vandal, crimson penta), Arum Spinosa, Sporothrix, Vandal Lato/Braton, FOMO weapons (baro, logins, events), Hate/Despair/War, or the Duviri melees are still much worse to grind than the modular stuff imo.