Lesson time.
Dragon Ball is owned by a combination of Toei, Shueisha, Bird Studio, Bandai and Fuji TV, all parties have a say. Early numbers for F and it's merchandise were really big and the production committee for the movie decided they wanted a new TV series to sell merch. Buu Kai was ending in July of that year so presumably it was decided that was when the new show would start, one problem, July was only a few months away. The earliest production material I can find is expression sheets for characters dated March 30th, 2015, which lines up pretty well with when the F merch started coming out. At best the series had 4 months (possibly only 3) from start of preproduction to airing, which is less than half of what a show should have. Keep in mind this isn't all Toei's fault, as mentioned above they aren't the sole controllers of the IP, Toei isn't dumb and most of their shows have pretty solid production schedules, it was most likely decided by the others that Super would start in July and Toei had to comply.
Toei doesn't cheap out on Super's animation, they actually spend a lot on the show. Episodes almost always have 2 or more animation supervisors, which is expensive, it's not uncommon to see assistant supervisors on episodes that aren't huge, they spend a lot on 2nd key animators and they take every key animator they can get. Super is probably Toei's most expensive show, the issues come down to the small amount of time the staff has to do their jobs as well as the fairly small core staff. Here's something many don't seem to know about the anime industry, outside of the more slave labor like studios, if an animator doesn't want to work on a project they won't, and this is especially true for freelancers. Super has traditionally be an unappealing project to work on due to the short deadlines caused by the show's production, so many animators just don't touch the show, or show up once and never come back, and this isn't even bringing up the huge shortage of animators in the industry right now. Money doesn't mean better animation.
Often times people say Super should just be given to a different studio, well that wouldn't fix the production issues the show faces and unless it was given to a studio that literally works their staff to death it probably wouldn't make any difference to the quality of the show. Fun fact about Toei animation, they are the only anime studio in Japan that has a union, they also pay animators based on salary instead of per cut of animation. Toei treats their staff well.
Also fun fact, the head of Toei's animator's union works on every single odd numbered episode of Super.
Another thing people say is that they should just put the show on a short hiatus to fix the problems. That'd be great, if they could do it. Super is making A LOT of money, I doubt Fuji TV or Bandai would be okay with the show going off air for 2-3 months, same goes for the sponsors. Ultimately it's up to Toei to fix Super's production on their own while the show is still running, which is no easy task.
I've spoken a lot about animation, but keep in mind that Super's production problems have been on all fronts, not just animation. Preproduction, planning, writing, storyboarding and post have all be traditionally rushed on Super. Whenever Super can reuse production materials they do, for instance most of the cast is using character design sheets from Battle of Gods and Resurrection F with a couple using their Z design sheets. Even things people wouldn't think about are recycled when they can, the interior design of Capsule Corp uses the design sheets from GT for example.
Super's production has been improving as it goes because they are able to do more preproduction with each arc, get scripts done earlier and they continue to grow the staff. The most recent arc is actually pretty consistent and we are seeing the staff grow fairly quickly. We somewhat recently learned that the scripts for episodes are given a normal 3 weeks to be written now and are written 4-6 months ahead of airing, which is pretty good on the upper side of that. On top of that animators have generally had more time to do their work thanks to there being more animators and animation supervisors generally have 8-10 weeks between their episodes as opposed to the old 5-7. Super still has a ways to go, but it's seen clear improvements to its production with every arc and that won't stop until things are totally normal. The work Toei has done and continues to do to fix Super's production is actually really impressive and the show's future looks pretty bright.