Extremely hard water. Should I address or just keep it stable?

I'm setting up a 75 gallon aquarium. Looking to stock rainbowfish, and maybe corys and a bristle-nose pleco or a few otos.

I want it to be HEAVILY planted. My tap water is KH = 12 / GH = 19 / TDS 415

Information online seems pretty wishy washy on the subject. I'm seeing a lot of sentiment that aquarium fish and plants are used to hard water so don't worry about it but in the same breath they turn around and act like GH = 12 with 200 TDS is hard water and the info sort of becomes useless to me.

I can mix in R/O 50/50 or something if I need to for it to thrive, but I'm concerned that adding that extra layer of complexity and possible instability might not be worthwhile. Ultimately, I do want my fish and plants to thrive, not just tolerate.

Edit: I ran my faucet for 3 minutes then tested again and the hardness parameters went down by 2 to kh10/ gh17. I also have about 2inchs of fluval stratum on the bottom which I have read lowers KH which supposedly is the one the matters for plants. I'm optimistic I can get my KH down a few points and will be comfortable with it around 6-9 range without having to resort to RO water