If you must have the panoramic windows then you indeed are limited to the infrequent named trains. I've never taken the hermetically sealed named trains but have loved my rides on those lines. I use the frequent un-named local trains which run on the same tracks and take just about the same time, but have opening windows, lots of people in second class (like me), better photo ops, and big but not panoramic windows and no tilting wine glasses.
You can check the timetables online, and mix and match trains. If you don't use the reserved seat panoramic cars named trains, you can pop off at an interesting station and get on a later train to continue but not if you are on the posh trains.
It may look when you look at the timetables that the named trains make fewer stops. The line is only a single track with passing places at the intermediate station. The first train to the passing point will wait for the other to arrive, the named train sometimes just sitting there in the sun, the stopping train will call at the station.