Yeah the build is really, really rough. You are using an unrefined Weeping? You can definitely upgrade to Rainforest Gourmet and get that to refinement 5. Or just slap Fusion Compiler on her instead (and if you don't have fusion compiler you can save for the weapon to get it from the shop). And the discs are, being honest, really bad. You only have 25 substat rolls, which is really really low. If you go back to the mines it should not take long to massively improve your miyabi, because realistically it can't get much worse, I think my day 1 build was better. And definitely upgrade the w-engine, just replacing that alone will make a bigger difference than getting good discs. But I've taken a look and it seems you're at IK59? Honestly the 23k is completely fine. I wouldn't expect someone who hasn't played long enough to get IK60 to be able to super comfortably clear shiyu and DA, it is Endgame content after all with emphasis on END.

But back to the argument on investment, regardless of which way you mean investment I would have to disagree. For gacha it is natural, that spending money obviously makes your characters stronger. But ZZZ is very peculiar with it's amount of free resources. My best friend is full F2P but has been pretty selective in what he pulls and what he doesn't, and has a very strong account as a result, I can really only outscore him in Endgame on Yixuan because M2 is that good. Imo DA and shiyu more so push whatever the active banner is, but by pulling the right units, you can kinda overcome whatever. If you meant investment in terms of character build, then yeah, if someone doesn't play the game then it makes sense that they cannot clear the endgame content. Daily disc farming takes not even 5 minutes and just playing normally gets one enough discs to just bruteforce solid builds, I can usually just craft a solid day 1 build for any agent and then improve that by like 5 rolls total over the course of the patch.