Do MNCs generally provide higher pay compared to start ups for a similar perhaps mid-tier (definitely not comparing CEOs LOL) role, such as a senior associate?

Yes, definitely. While I was looking for my second job with 2 years experience, an MNC can offer $4850, 16.3% increment. 2 small companies (not start up exactly, but SME), gave me pay cuts and can only offer $3500.

Source: job offers from Aon, Wah Hin