This is an interesting theory, but I think you’re just wrong on several counts. There are definitely permanently online people who don’t do anything in the real world, but out of the groups you listed, vegans and MAGA members almost universally have material impact on the world (socialists and antivaxers would like to, but their impact is usually hyper-localized, so you’ll find more “only-online” types).

For vegans and MAGA, there is real direct action that they partake in as buy-in for the group. For the former, it’s abstaining from animal products, and for the latter it’s (at least) voting for Trump.

Claiming most vegans or MAGA people aren’t motivated to improve things for their cause is incredibly foolish. Like I said, an interesting theory, but it’s just materially wrong.