Thinking that Fubuki is stupid for not boosting the more powerfull than her Bang is, for me, missing a point that goes in the series.... Most heroes care shit about other heroes.... They mostly don't know the real power of the one standing next to them.... The prime example of that is King.... He is a S-Rank Hero by sheer luck, but doesn't have the power to back it up....
Fubuki knows who Bang is, knows that he is a S-Rank Hero, but migth ignore just how strong he really is.... She migth thing that he got that rank at his prime, 50 years ago, and now only has the title for it... She definitely doesn't know who Bomb is. So she really doesn't have a clue that by just supporting and buffing them they may have better chances of doing shit...
Another example of the ignorance of powers can be seen in chap 89 (hotpot), where she insults Genos, another S-Rank, and doesn't bat an eye over it. She knows that Saitama is stronger than her, but that's it... She doesn't realise how much...
I thing that she migth have a new point of view after all this