I think back then, people usually kept the speed of their attacks in speed equal if it was different from their own.
Aka Gal would be equalized, while Sirius Laseray Sorcery would still be SoL. I'm not sure if things changed since then, though. So I won't say for certain on that front.
Marco's Pseudo-Flight give him an edge in mobility, but it's not something Gal isn't able to fight as he showed that even in the fight against Svectral, where she was flying around at high speeds *and* mixing it with Vector Sorcery to get the beams out but Gal kept bending them back with Gravity mid-trajectory to tag her until she bended them in Laz' face as a last resort. Thus he can deal with that stuff.
There's the lifting strength for what DMUA mentioned...
Being an adventurer in this setting, where Flora users can also absorb Light and Sunlight to varying extents and sustenance, I think his sensing would catch-up relatively fast to the Sun Stone (which is listed to have power of its own) and that there's a kind of similar thing going on with it.
I'm not sure if he would actually have plans on destroying the stone, keep his focus on Marco or try both at this point.
Skill-wise, Gal should not be lower (or anywhere near for that matter) Beginner Class adventurers, who can usually fight martial arts masters, samurais/master swordsmen or ninjas on even grounds and match their skills by default (Martial Artist, Samurai/Master Bladers, Archers and Ninjas are all classes that by the time they are actually accepted as adventurers, can do pretty nifty stuff like making arrows bounce off multiple times from pretty much any kind of surface (Archer), cutting stuff that's not quite within their sword range by skill alone --- aka cutting stuff in a manner such that a 'distortion' from the blade swing can be focused to cut something as small as a falling leaf in the limits of their eye-sight), Shintokei, fighting multiple opponents/monsters at once if they are even in power but not as skilled and such things.
With this in mind I'm leaning to vote Gal atm, all things considered. A pretty straightforward match, but interesting!