It’s not new; Rider 2’s helmet has been going back and forth since at least the 80s.

1): Why is DiEnd's World based on Missing Ace?

2): Why are the Roach of DiEnd's World based more on the Blade series Roach as opposed to the Missing Ace Roach?

The only explanation I can give you is the fact they got the Missing Ace Riders actors back so they made Diend origin based off that movie. The roaches thing was probably just using whatever suits for mooks without really thinking of it.

Because Decade’s original writer left the show and the new guy just ran out the rest of the series by pulling stuff out of his ass.

Decade's' writer left the show? When? Genuinely curious.

He left after the Agito arc. Shouji Yonemura of Super-Hero Taisen fame took over head writing duties after that, which explains why the show's ending was such a complete clusterfuck.

That... explains alot, actually.

The ''finale'' was pretty awful(I mean what was that?!) but then I did prefer things like the Shinkenger and the Black/Black RX teamup to most of the regular tribute episodes so there might be a tiny bit of swings and roundabouts with different writers.

Are there any reason why Kabuto and Faiz are rather popular? I mean, those two are the first to receive their Figurerise, and Seiji Takaiwa in particular is fond of playing them. Maybe because those two are where he could be as expressive than any other Riders before?

I suspect they are just "safe bets" for testing a new line out. They have reliable popularity and sales. Kabuto already had some engineering from the original Figure-rise line and Faiz was voted the #1 series in a Japanese poll from 2018 https://tokusatsunetwork.com/2018/09...-rider-series/

They were among the earliest releases in the Shodo series, and CSM belt line, which makes me think they are just flatly popular. If Hiro Mizushima wasn't blacklisted by Toei, I bet we'd see as much of him as we see Kento Handa in the crossover movies.

They are also just really good looking suits!