As a hiring manager, if someone shared a profile of a person with a PHD in earth sciences and 8 years of “full stack” experience I’d immediately assume they were a generalist with surface level familiarity and no mastery or depth in any one area.

I’d then look over the profile trying to disprove my assumption. Lacking a very strong signal in mastery of something, I’d pass on the profile.

Only at small scales are full stack engineers valuable. Their value is not in the quality of their output but in their ability to deliver make shift with that avoids having to pay for specialist who can deliver quality.

Assuming there is product market fit then generalists are replaced by specialists. This is where the true value aligns in terms of high quality output being compensated proportional to value created.

Given all this my advice is to pick two complementary areas, specialize in those areas and develop deep mastery. Keep your broad general skills. Then market yourself as the T or H shaped engineer that’s most valuable.