Buy side analyst roles typically have less good comp to begin with, but the upside is also greater. At the end of the day, if you are one of the lucky few that can generate (positive) alpha, then the sky is the limit. On the sell-side, you can’t make the really big money because you’re not making anyone any money (directly).
20% bonus might be right at a conservative firm, experiencing mediocre performance, for a first year. Or perhaps for someone working in a sort of satellite office (e.g. not in London, if you are in the UK). Otherwise, very low and a bit of a ding.