When it comes to surrealism, nothing Rider or Sentai have done can ever touch the early Metal Heroes shows, especially Shaider.

Why we don't another space-themed sentai ?

I dunno, have you seen the Ohranger movie? :lol

EDIT: oddly enough, it looks like Uehara wrote both Shaider and the Ohranger movie. Huh.

Should sentai could had cosmic beings like marvel ?

If you mean "cosmic" in villains; The Zyurangers fought Satan, the Magirangers fought Cthulhu, the Gekiranger's fought an ancient demon kung fu dragon monster and the Abaranger's fought whatever the hell Wicked Life God Dezumozorlya was.

I'm not sure if you've ever even watched Super Sentai.

Well, Satan and Cthulu aren't really the types of monsters to come in mind when one says "Cosmic being" since they're more akin to demonic entities. Gekirangers' final enemy was more mythological than cosmic.

This isn't to say they haven't fought cosmic beings (2/4 of Gosei, Daijinryuu in Dai, etc). I just think when someone says "Cosmic forces" they're referring to magical alien style characters, rather than enemies from space.

In which case a lot of the 80s Sentai villains fit the bill.

Yeah, I was curious about what others think of when they hear of a cosmic force.
Like, the Zangyack from Gokai are aliens, but they don't come to mind for me.

Exhaus from Carranger could be considered a cosmic being too ?

Is Birdman's Role a wild card one?

I wouldn't say he's allies or an enemy to Zyuohger because he save Yamato twice but he despise Zyuland

You don't know, He could be a good guy or a bad guy.