Bike transport while touring - would a folding bike be better? So I’m thinking of touring with my  lovely self made diamond bike with 28” wheels that I built from used bike parts. I love to ride on something that I built but I wanted to be able to tour a lot and I had some doubts when it came to traveling with a regular bike because of in-between modes of transport such as putting the bike  on plane, bus, train or car, but I’ve never actually done a prolonged tour via bike.
My question for any experienced tourer is: since in-between transport for me is a must, does a folding bike like Brompton really make a difference compared to maybe disassembling a diamond shaped bike every time you want to go on train/bus/hotel?
I don't think there is a simple answer.  It depends on the touring you want to do and your tradeoff between transport trouble and riding trouble.  My wife and I went on a guided tour in Spain where we rented bikes from the operator but one couple brought their own DF (diamond frame) bikes.  They had a fair amount of trouble transporting the bikes-on the airline they were oversized cargo, they couldn't take the high speed trains, and getting taxis from arrival to the hotel was a challenge.  On the other hand, they had bikes they love.  The same operator does more challenging tours where the majority of clients bring their bikes.  This wasn't even touring as the operator moved all the luggage once you were on the tour.
I suspect once you have decided to bring a DF bike, the rest of the gear is big and heavy but doesn't make it too much harder to manage.  You need somebody to help you with luggage and once you have transport for the bike and a helper for luggage you can bring what you are willing to ride with.
If you get a bike that is easier to transport than a DF you are trading bike performance for ease of transport.  Depending on the tour you are doing I suspect the ease of transport is elusive.  If you carry 20kg of gear when riding, can you carry the same 20kg plus the bike when you are going through airports, taking trains, etc.?  If not, you may save the oversize baggage handling but you still need someone to help you.
I don't think a more transportable bike is silly, but I think you need to consider the whole transport approach.  If you get a smaller bike, the consistent thing may be to pack much lighter to get the ease of transport.  Do you want to do that?  How many changes of clothes does that allow?  Are you camping?  I suspect it is hard to justify a smaller bike if you are camping.  On the other hand, with a light load you might make the transport easier.