If you want to stay with the Mini, I would wait for the Mini 5, but that will be sometime next year. The Mini 4 just uses an overclocked A8 processor so might not even work anymore. The 6th gen 2018 iPad, not the Pro, uses the A10 processor so buys you a year or two of use before it’s obsolete. (I think the full-size iPad is actually cheaper than the Mini 4 as well.) You have to figure DJI isn’t going to make its software less complicated and more efficient in the future so... Someone else might have a different experience and opinion. I’m giving you my experience with the equipment. Once you upgrade your tablet, flying will be much more enjoyable. Trust me there.
FYI- even with non-DJI mapping software and auto-pilots, the processor still needs to be robust.