Since pfizer and moderna are both mrna vaccines, why is pfizer more effective with the elderly, variants, and severe disease? is the pfizer vaccine better?

All three vaccines were studied at different times in different populations. One is NOT necessarily better than the others unless one separates out the statistics, and presence of local variants. Also, need to account for company promotion, and media distortions. In the end, get vaccinated with whatever is available and don't try to rethink the FDA's approval process.