<<"You have to be able to carry your suitcase yourself up a very long staircase (this will happen somewhere on your travels). ">>
I don't disagree in principle, but, in practice, in Switzerland, whenever I have been at an inn which required taking a bag upstairs, the person at reception always offered to carry my bags up stairs. Unfailingly. As I have gotten more set in my choices of inns over the years, I have tended to pick ones with elevators (lifts). But, I still find ones without such modern conveniences. Some nice old ones in the countryside are that way.
And, I will not say that 100% of rail stations are equipped with elevators or moving stairs (what we call escalators here in the USA). I will say that they are common. In the stations which have maps on the SBB website, they show on the station maps. And, some of the older smaller stations, in the regions rarely frequented by tourists, I still see a smooth ramp perhaps 30 or 40 cm. wide beside the stairs, to allow a wheeled bag to go up or down.
<<"Rick Steves has a video on packing light (and Sarah Murdoch for women) both which might be a bit extreme ">>
As you imply, Rick does not pack for some important elements of travel. He definitely does not wear the very large size of hiking boots that I do. They take a lot of space. I can't wear them on the plane, because my sciatica demands that I get every single fraction of an inch under the seat ahead of me for my generous sized feet. He probably does not try to fit a hiking staff in that bag ( although there are collapsible ones). I think that he does not need to take a set of dressier clothes, which I find useful, desirable, or necessary for concerts and some of the better restaurants. I am graced with friends who take me to some of those, and I find it nice to be somewhat better dressed than I am for more ordinary places.
With all that said, my point is that it is possible to get around with bags a bit larger that what Rick recommends, because I do it all the time. The worst part, consistent with your comments, is that some of the trains have narrow doorways with steps. They are a nuisance with a bulky suitcase. So, I have found that a large duffel, bag with wheels, is easier to maneuver in such situations.
Oh yes, one other minor point. While we have laundromats ( public self service laundries) almost everywhere here in the USA, they are scarce in Switzerland. The Swiss apartment buildings generally have laundries for their occupants, which reduces the need for free-standing laundromats. So, for a 3 week trip, or even for shorter ones, I find a way to schedule some clothes washing. Jetwasch in Luzern often fits my schedule. Many inns will do some if you ask, and generally don't charge big-city hotel prices.
It's been a while since I read one of Rick Steve's books, so I don't recall what technique he uses for having clean underwear. On occasions in the past, I've washed some undies in the sink, but, It's not my favorite method. ;-)