While GATG may not have as much appeal as the original show, it was able to execute one thing that the og couldn't. And that was Gadget's sidekicks.
We all know how bad Corporal capeman was, he's an asshole, he's annoying, and he overall jus freaking sucks look at him.
Ew. Another issue (aside from his character) is that he's out of place. Cause his whole thing is that he's a "superheroes sidekick" or something, and yes while Gadget is technically a superhero, it doesn't feel right seeing him work with this guy. It ruins the 'scifi-ish cyborg detective' theme.
Fidget and Digit on the other gadget-hand fit well with the theme. Being lil robot mini versions of the Inspector makes them blend with the show's atmosphere perfectly, both shows in fact. Cause if you put the Gadgetinis in the Original show they would still fit.
We know Gadget prefers to work on his assignments alone (even tho that's hardly the case in reality), but if he had to have companions on almost all of his missions I'd think he'd choose the Gadgetinis. Cuz
They're equipped for the job like he is (I'm sure he still has way more gadgets than they do but they're probably equipped enough)
They're durable robots, so he doesn't have to worry about their safety as much as he would with Penny and Brain (since an organic life and mental health is more fragile than the gadgetinis. Specially if your a child like Penny who shouldn't have to deal with the burden of M.A.D in the first place).
Knowing Gadget. Having little robots who not only look like him but, are programmed to bring justice to M.A.D alongside him, and help him even without him knowing, is probably very awesome for Gadget. He sees himself as a teacher/father figure to them and I wouldn't be surprised if he takes alot of pride in having sidekicks created by his dear niece (I just know he's super proud of her).
The only reason Capeman became Gadget's sidekick is cause he buttered him up.
And most importantly, the Gadgetinis are actually enjoyable and fun to watch. They are comic reliefs who are sassy and silly. They have a funny dynamic.
While it's still a bummer that they took Brain's role, they make up for it by being way better sidekicks (and better characters in general) than Corporal capeman ever will be.