Why do you believe a cooperative would have been better?
In general I prefer cooperative work and have experienced too much antogonistic work in startups.
> A 2013 report published by the UK Office for National Statistics showed that in the UK the rate of survival of cooperatives after five years was 80 percent compared with only 41 percent for all other enterprises.[5] A further study found that after ten years 44 percent of cooperatives were still in operation, compared with only 20 percent for all enterprises.
> A 2012 report published by The European Confederation of cooperatives and worker-owned enterprises active in industry and services showed that in France and Spain, worker cooperatives and social cooperatives "have been more resilient than conventional enterprises during the economic crisis".[47]
Source: https://en.wikipedia.org/wiki/Cooperative#Economic_stability
As just another data point, I've had fantastic experiences in startups.
It really depends a lot on the people you're working with, and if you're a good fit.