Fake Steve is right. Gastonne mainly just gives you access to galleon. He does have firegroup spell, but that means your not giving 3 focus to galleon. Durgen feat and explosivo make for some nasty ranged damage. Explosivo also means lady aiyana and holt aren't auto include which frees up 4 points. But, I am taking tact corps just to keep durgen max focus mostly so I am wasting 4 points .
I think durgen would drop MHSF like JR drops pig jokes. Raven MHSF might get some shots off, but no way they make it to Gastonne.
For 20 things going on , not really. Gastonne gives 3 focus to galleon, dougal gives artillerist...rinse and repeat.
I mean I coulllllldddddd 2 focus, feat, firegroup, extra powder ration, explosivo....thats only like 6 extra things so like 8 tops. If I explosivo and feat the harpoon has a really good chance of hitting high defense at 19" away.