lunarity gain is to low after the first rebirth
That probably means you’re over-stressing the character; if you get too much “Dubious” you stress out before you’ve gathered enough Solarity to convert to Lunarity. I’ve found 3 copies seems to be the sweet spot for the early game, 4 if you want to end a run prematurely.
Dubious as an upgrade trades longevity for speed; you get 3x (4.2x after upgrade) Solarity, but 10x more stress (for 3.33x less Solarity-per-stress total). It makes the run faster, but gives you less out of each run.