Show with little to no progression? Tick.
The majority of the cast are cut from being actively involved in the story, not even knowing about Gridman, Digifer or any of the battles for like 3/4 of it? Tock.
Focusing episodes on one-note preachy messages without giving characters actual depth, rendering the entire point of making it SoL meaningless in the first place? Tick-tock, goes the clock.
If anything, episodes like Lonely Hacker show that Gridman NEEDED to take itself more seriously, but was too afraid to, so you end with chickenshit endings where instead of helping a PTSD-riddled kid with his social anxieties, it has Gridman magically curing him of all his problems. This is what waste of potential is.
Just because something is fleshed out doesn't mean it's good.
It means people put actual effort into show's characters.
The focus of your argument was life slicing portions.
It was that Takatera knows how to make grounded SoL-focused tokusatsu compelling. Which includes heroes being pushed to their limits and having to actually put effort to win frequently.
And that's a bad thing because....?
Because separating your antagonist the from heroes for 40 episodes isn't interesting. Kuuga managed to make it work by keeping a lot of stuff about Grongi vague (since they're supposed to be an unknown civilization with different culture), so viewers were learning about the show along with heroes basically. And I still think it needed more personal conflicts between MC and villains. Gridman doesn't have much going for it, so it misses out on the biggest opportunity to develop both heroes and villains. Except in the end it wants you to buy that your villain has developed, so it tries to have it both ways.
You mean high quality animation?
Around 70-80% of Exkaiser "high quality animation" is stock footage. And even that aside, it's far from a the only show with good animation (even in its own franchise). so why should I waste 50 episodes on disposable one-note plots, which are realized better in actual slice of life shows anyway? At least Eldrans tried to have fun antagonists with personalities. Exkaiser couldn't even manage that.
Hey that's cheating, Fighbird is the best entry of the franchise. Compare it to Might Gaine or GaoGaiGar at least.
I like Fighbird, but it's definitely not the best Brave entry. Might Gaine is a much better contender for it actually, but really all Braves that are not Dagwon OVA are better than Exkaiser.
Toku shows aren't supposed to be too serious, Amazons tried that and it was real bad.
Amazons tried too hard from what I've seen, but generally being serious isn't an issue with toku. If anything, the opposite is true now, because one of reasons Saber's failing so far is prioritizing bad gags over giving characters actual personalities. Most of post-Hibiki shows are afraid that viewers can't cope unless there is a gag thrown their way every minute or so (Kabuto, Wizard, Ex-Aid and Zero-One had it the worst).