At my current company, everyone is simply a software engineer and you are paid based on your value. Everyone seems happy with the arrangement.
I also work in a flat company. Actually some weeks ago, one of my colleagues was applying to a new credit card. So the bank called our HR team to very a colleague's salary. I ended up taking the call due to a mishap on the phone system. So they needed to double check her salary, because she had mentioned 50% raise but no change in her job title. So I had to explain that's the way our company is.
I would expect them to push for a Marxist view on "value" of work, basically each hour is of equal value, but where you adjust for number of years of formal education, again where the type of eduction is not important. A developer with a MSc from a top college may be compared to someone with an MSc/MA in Sociology, working in the HR department, for instance.
The key alternative is to gauge value based on market demand, but where I live (Northern Europe), those who advocate "equal pay for work of equal value" don't seem to go for that. Instead, they claim that nurses and engineers should have the same salary, as the length of their education is different, at least for people employed by the public.
Maybe full transparency would solve all those problems (eg. all paychecks are public), but i know people who prefer their paychecks private, because of otherwise modest lifestyle, their landlords would increase their rent, and random family members would come begging for money.