Roger
He/him
- AKA
- Minato
The purpose of the story is still to tell its own story – Rebels is telling a story about growing up, gaining a family in those who are closest to you, and ultimately learning how to stand up for things you believe in, even when you don't rally everyone else to your cause.
It's not reductive to the story that the characters in it also serve the purpose of fleshing out small details of other characters & events during that time by selecting backgrounds for them that allow them to naturally be in a position to explore those things that people already know and find interesting. Not every story needs to exist in a complete vacuum – especially those in Star Wars. They're using the setting to embrace it, not to shy away from it, as that's a core part of storybuilding in a connected universe. Rebels is a group who is a focal point for those interactions because of the character's backgrounds and connections to existing elements of the universe at the time. New characters don't need to bump into every legacy character possible, but they also shouldn't be permitted from doing so if it makes sense and is telling an interesting story that serves to develop all the characters involved.
I don't feel they were in a natural position to do that. The characters they meet up with would go on to believe Obi-Wan is their only hope. And there after, hang out with Luke for whom opportunities to learn about the Force and the Jedi were not available outside of finding Yoda. Ahsoka, personal friend of Artoo, Bail Organa and so on makes that problematic. The opening crawl of A New Hope tells us the Rebels have just won their first victory of note over the Empire. Rogue One tells the story of those events, Rebels however has Vader, Tarkin, Thrawn, Yularen and the Emperor himself turn their attention to Lothal, and sees them defeated and ousted on a planetary scale outright. Then there's Lando happening to come across these characters within a week of Leia, Hondo meeting up with them within days of Ahsoka and so on. I see praise for the Mandalorian for making the universe feel bigger for having people that don't know Jedi or the Force of what exactly a Mandalorian is. Rebels makes the galaxy feel quite small.
Also, Stormtrooper accuracy jokes are literally all over in Star Wars stuff. I'm not sure why you're picking this out – but again, this is why it's important to have watched something before you try to criticize it. Both of the times those sort of jokes occur in the series are specifically to make a juxtaposition to demonstrate the differences between the regular Stormtroopers who are essentially grunts just interested in a paycheck, from the elite military individuals like Imperial Sharpshooters & Death Troopers that were also a core component of the Imperial army.
Rebels and the Mandalorian are where the accuracy of Stormtroopers became a joke characters in the universe itself might tell each other. Disney had a choice when they acquired the licence, to treat the Stormtrooper seriously or play into the joke status they have among the fandom. You can like their choice, others might not.