Nah. Pica isn't that dangerous. He is only dangerous in very specific circumstances. At sea, Pica is nearly totally useless.
Its also worth noting that I think Oda was trying to convey that Bellamy was heavily injured after the match, and thus really shouldn't be used for that sort of scaling stuff.
In terms of this specific circumstance though, Zoro's bounty after Dressrosa was based around the fact he defeated Pica, so I don't see why its unfair to assess Pica's bounty in relation to how the marines percieved someone who defeated Pica.
I'll put it this way. Bounty isn't exactly power scaling. But in specific situations where characters literally have their bounties increased off the sole fact that they showed their strength against a specific opponent, I think its more than reasonable to say that the person who their new bounty is being based off would probably have a lower bounty than the person who beat them.