If you have copper pipes I am pretty sure you can add a ph adjuster to your RO water and things will be ok. If you are not limited on supply I think RO is the way to go. Cost has come down considerably from ten years ago.
You are exactly right. My well water is so hard you can hit it with a hammer. Anderson pump house put in a full house ro 4 years ago. Big up front cost but fairly cheap to run after that. I am still on my first pail of antiscaleant and use a couple bags of soda ash a year to bring the ph of the water up to neutral. Just changed the membrane for the first time a couple weeks ago. Best part about it is every sink, toilet and appliance look like new yet.