Yes, very good point. I definitely recommend the Tamiya grey, but use it wisely! Actually, my main trend for awhile is to avoid putty..."cheat" byt scraping plastic around area to blend and use as little as possible, and in some seam-filling applications, use CA (superglue) - tho that is much harder than the surrounding plastic. At one time, years ago, I experimented with styrene shavings (really "sawdust" mixed with solvent. Good in theory, but without machinery it's hard to homebrew it.
Anyway, great work, and good on ya for attempting something new and tricky. if it doesn't work the first time, you c an do it again! But by your progress shots, I'd say it's working fine.