I'll agree with you that character design and backstory isn't amazing right now, but the root cause of it ultimately trickles down to three things in my mind:
1. For animes that are based on mangas or light novels, which is over 60% of animations, it's simply impossible to cram all of the details from the written material into a single season or two of animation. My thought is anime studios are leaving some of the backstory aspects of characters out of the anime, to help provoke a desire to learn more about the story setting from the viewer, and cause them to want to buy the manga/novel to learn the rest.
Two recent animes that I've fully kept up with the mangas on were Masamune-kun no Revenge and ReLIFE - both fantastic mangas. I'll admit that the mangas are hands-down better than the animes because they fill in a lot of the character development holes you'd otherwise notice in just the anime. Plus, buying the manga helps fund the original artist, show your support, and help them produce more quality work - what's not to love about that?
2. It's becoming increasingly more difficult for novel/manga/anime writers to come up with original ideas, just because they have to try and make something fresh in light of 50+ years of existing anime ideas. This is true of storylines, universe settings, and relative to your comment, characters.
Generic characters are more prevalent now just because so many of the ideas for making unique characters have already been done, leaving artists with limited options for originality. One of the guys I know personally who does this stuff for a living has commented to me before that he's about to the point of ripping his hair out on some days over this. "I can't use that hairstyle because it's already been done before, I can't use that eye accent because it was used in this anime, etc." I don't think there's going to be an easy solution for this aspect, to be honest.
3. Anime is starting to progressively struggle more and more financially back in Japan, and you'll find that consolidation of studios is starting to occur on a widespread level over there just so artists have a higher chance of making a decent living with it anymore. By consolidation, I'm referring to the idea of smaller anime studios getting bought out by the larger ones. The number of anime studios in Japan is progressively shrinking as smaller studios are finding that it's more difficult to make a living in anime, end up filing for bankruptcy or outright selling their studio, and the larger studios are hopping on this because their reputation is what's keeping them alive in the industry.
If you're working in a corporatized anime environment where costs have to be minimized and profits maximized, you'll find yourself cutting corners in some aspects to try and streamline services more - because that's the main thing your manager cares about. Many design aspects have taken a hit in light of this, as you've noted.
I don't think there's a fix for these things, and I wouldn't be surprised to see them worsen in the next few years unless someone steps in and changes the way that the anime process works over in Japan.
depending on the budget for one animation project, some are a good for doing adaptation but some you can tell they just rush all the works to adapt one story and it's disappointing for the people who expect an adaptation but it's lack of justice to the story especially if the there's a lot of battle in the story its like your imagination is much better than the anime