Re: To gun fu or not gun fu?
You are right to avoid gun foo.
If your player wants to play a master of firearms, skill levels and extra damage dice are the only fair way to go. and by fair, I mean fair to the other players...the ones that you made pay full price for their powers.
Here's why: Two ways to write up a 6d6 EB with +2 vs range.
30pts 6d6 EB "Ray Beam"
4 pts +2 Ranged Skill Levels with "Ray Beam"
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34 pts
vs
15pts 3d6 EB "Ray Beam"
4 pts Basic Shot (+2 Ranged Skill Level, +3 DC)
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19 pts
You could argue that the non-marital arts example should cost more because it can be used with Haymaker, but is that worth 15 points? If I were the guy that you let buy the martial arts version I'd spend the points on +5Dex and not even bother to kiss Haymaker goodbye on her way out the door.
You could also argue that the problem with ranged martial arts affects normal martial arts too. You would get no argument from me on that point. Martial Arts has always been broken in the hero system for the same reason as noted above.
16pts +4d6 HA "Mighty Fist" (total 6d6)
5pts (10 pts) +2 DCV -1 limitation "only after Mighty Fist"
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21 pts
vs
8pts 2d6 HA
4pts Martial Strike (comes with +2 DCV and +2d6 HA)
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12 pts
If you're playing in a talented normal game, Martial arts is a good fit for the simple reason that super powers aren't available, but once you cross the boundary into super land you should leave MA at the border - they have no place there.