Ill be honest and say that the spreadsheet is too much info and i got lazy reading it so ill just answer the ones on top of my head.
For starters, water and light catastrophes are way harder than the ones we have right now (thunder rag is literally a joke), so i dunno what you mean by "a bit easier to different", maybe i got that wrong but still wanted to clear that out, that being said, the weapons depends on your team, it has been said many times (maybe not here, i tend to mix discord with this forum since dc is faster) that theres no best weapon, its situational based on each team, ofc there are some good ones that you can call meta (shingen morgan herc), but choosing any one of them is personal choice and thats your homework.
This always triggers me but ill remain neutral, being a mono element user just makes things harder in the long run (and you start falling behind the progression curve), maining one element and focusing on it until its maxed is fine, since that works as your wild card for any event and stuff that the game throws to you (most of the time unless elemental disadvantage), BUT please for the love of god stop focusing your entire life on that single element, thats beyond retarded, if you are done on 1 element, move to another one, its common sense, your goal is to have 6 grids maxed, not 1.
Dual weapons with FLB, better eido grids, better accesories, it all sums up.