> 'Radical' is synonymous with fundamental

That is not at all what 'radical' means in the context of 'radical sub-culture'. The definition you're looking for is one of:

2. thoroughgoing or extreme, especially as regards change from accepted or traditional forms: a radical change in the policy of a company.

3. favoring drastic political, economic, or social reforms: radical ideas; radical and anarchistic ideologues.

I guess you could argue that trans people fall under definition # 2 from the perspective of many (most?) people, but i also think that 'radical sub-culture' generally implies some kind of conscious action — i don't think that simply existing as a member of a minority makes you inherently 'radical'.