heliduck
You might be overthinking things (no demerits there!) but managing one's career is obviously a very personal thing, and done in light of objectives, both personal and professional, as they come to view. My 40 years of flying helos, military, then civil - half for operators, half for corporations, found only one slight bump when applying for a job. That was being identified as a "Northeast pilot", meaning, I guess, having worked in the NE US as a corporate pilot for 18 years. In one case it was a show-stopper on resume receipt - no discussion, no nothing! Some day I'll figure that one out but I really could care less. At another involving application to fly large helicopters having a balance of flying many different types, including @3000 piston, a lot of light turbines, and almost all the medium twins to date, in many environments, etc., led to the application being considered quite acceptable. I guess variety was valued.
When I view someone's resume I try to develop a sense of who the person is first, then consider their experience in light of the air sense they are likely to have developed, then look at what variety of background they have lived, where they have worked, and lastly the type helicopters they have flown. Half of any job is doing it, the other half living with it. If I think an applicant is likely to be rich in both he/she gets an interview based on the most likely candidate to succeed amongst the resumes in front of me.
If an employer devalues what they consider too much piston time I would say they are not looking at the air sense the individual may have cultivated, thus shorting themselves a potentially great employee.
BTW, pistons are great fun!