> As a french, it is not muddling that I want but reasoning.

Huh I never noticed this peculiarity of English before. "I am an Italian/Australian/Canadian" - fine. "I am an English/French/Swedish" - hell no. Traditionally you'd say Frenchman, nowadays you'd avoid the gender and use "I am French" directly as an adjective.

Anyone know why -an words can be used as a noun and -sh words can't?

-an words are initially nouns that have come to be used as adjectives, while -ish words are only adjectives.

The English language readily makes adjectives from nouns, but not the other way round. Nominalized adjectives are used for collective groups at most (which is why you can say "the French") but rarely become regular nouns.

"As a french person" would be the typical genderless replacement, not restructuring the sentence entirely.

muddling through, I have managed to deduce that by 'As a french,' you mean that you are French, am I correct?