Interstates are utilitarian travel for getting where you want to go without much sightseeing, because you're hauling cargo or transporting your vehicle or whatever. Yes, there is some sightseeing. And if it's your first time seeing a new landscape it's always going to be awesome. But ultimately interstates are very insulating.
Road trips, as disjoint from interstates as possible, are a great way to see scenery, but they take time. Even two weeks to get across the country is too short. I'd say you want a month minimum.
Train trips are a nice middleground for getting a taste of the road trip scenery (but not the waypoints) within a short amount of time, where you have a little more time to spare than flying (several days cross country), but not much.
Driving works, but I'd much rather take a train. Too bad they are generally terrible here. I've been to Europe; it can work!
I've done plenty of long US road trips: Chicago to Seattle, Chicago to to East Coast, Michigan to Florida, Seattle to southern California, a loop of the southwest starting and ending in Vegas, etc.
I've done road trips throughout my life (Seattle to Socal was less than a year ago) and do smaller (~3hr 1 way) ones on a regular basis (Seattle to Portland or Vancouver). I've also taken trains in the US and in other countries and it's a different experience.
Having to focus on the road for more than an hour at a time wears you down. If you have a car full of people such that you can rotate drivers, it's bearable but that just means sharing the load. In comparison, in a train I can simply relax and enjoy the sights and the trip. If there's a beautiful mountain I can focus on it without worrying about a car or animal in front of me. If I want to eat or drink or use the restroom I do without having to wait miles to find somewhere to pull over. If I want to read or use my laptop or have a beverage (even alcohol if I want), it's fine.
I've driven Seattle to Portland dozens of times. I've also taken the train several times. When I drive, I arrive in PDX tired. When I get off the train I am invigorated and ready to start my day (even though when I've done it I usually had to get up at 4 to catch a 5:30AM train, times which usually don't exist for me and should seemingly leave me tired)
As far as exploring cities: while infrastructure in the US is bad, there is a strong correlation between cities worth exploring and some form of bus/bike/scooter rental. Train stations are also usually centrally located. If I want to explore I go walking and there's plenty to do within a few miles of the station. If it's further out I grab a bus. If I'm there for multiple days AND there are far-out things I want to do I could rent a car but it's almost never been necessary. Amusingly the only time I did a combination train-car trip was in Germany, where I wanted a vehicle to bounce between small towns the train didn't hit (but took the express train back from Berlin to Munich). In America it hasn't come up because the kinds of towns that don't have public transit are overwhelmingly either so small you can walk anywhere or so generic and boring that I don't get off the train except to stretch my legs.
Yes, I'm sure that folks can find counterexamples. I'll poke a hole in my experiment with East Lansing, MI: A fairly standard college town with a beautiful walkable campus.....and an Amtrak station in the middle of an industrial park a fair walk from anything good. Even then, though, it's a 1.5 mile walk to the middle of campus or 2 miles to the bar district, so it's still not the end of the world.