I've not done the Ventimiglia route yet (it looks nice though, albeit doesn't get that far into Italy). I have done the Paris - Milan line a couple of times on both TGV and Frecciarossa. It's a gorgeous line and I did get door to door to Milan in one day (needed a lift for the first bit as I had to start before the local buses woke up). Turin is even easier and a much nicer destination.
Your journey and mine were both really nice ways of getting to Italy and I do think people should try to do more journeys like ours and fewer mindless hops in aeroplanes, both for CO2 reasons and to reduce over tourism.
But I don't honestly think we will win many people over by claiming the train is a good or an easy replacement for the plane because for a lot of people it really isn't! Most people don't care about having a lovely, interesting, comfortable journey with points to appreciate stopover cities along the way like I do, and you obviously do too.
I've done a couple of talks on train travel to environmental groups and even when you're preaching to the converted, someone will say "my son lives in Cyprus can I get the train to visit him?" and you'll watch a room full of people look completely disillusioned as you describe a route that's theoretically possible but unlikely to appeal to anyone who doesn't have both time and money to burn.
I will keep plugging on with my train holidays. I really enjoy them, and I talk about them to other people who love the idea of doing it themselves (and sometimes do) but often find the reality a little bit unworkable. Until we stop killing railway development and subsiding the airline industry in thousands of stupid ways, avoiding air travel is always going to be a somewhat niche pursuit.