The reason the Boffs provide such a huge bonus is because they arn't adding their 20% properly.
When you enter combat your passive hull regen drops to a % of its normal value. I think its something like 15%.
However this 15% is being calculated BEFORE the extra 20% from the Boffs instead of after it. Meaning if you had 200% hull regen out of combat (100% base + 100% from 5 Boffs) you get 115% in combat instead of 30%.
This erroneous calculation is why Humans are being way more effective than they should be. Eventually they might get around to fixing this and when they do Humans will be useless again.