This is based on my own experience and opinions*
Saitama strength has always been way too strong since the first chapter till the final one.
He is capable of defeating any enemy with a single punch. Inside his universe there has been a large range of monsters, mutants, aliens etc.
That were really strong and could destroy citied with their attacks if Saitama did not destroy them with such facility.
He is strong a single palm can drive his enemies through various miles in distance destroying big buildings on its way. Yup a single PALM.