Maybe not the "right" forum for this, but here we go:
- Legacy carriers and even others, will inflate their tickets for one-way flights versus RT flights.
- if you want to fly into Paris CDG and go to Disney Paris with your kids, but take a train to Denmark to visit LegoLand and fly home via CPH, use the multi-city tool on Google Flights OR on the airline's booking page.
- your $2k plus oneway will turn into a $1200 RT via multi-city but connecting via CDG for Air France (as an example)
- I will personally pay $1-500 more not to do some insane routing via 3 cities to get where I want to go.
- You're taking a group booking, but you can get where you want to go in 9 hours versus 16... and everyone is paying individually... suddenly the $2,000 difference in price turns into $150-200 each, which (again in my opinion) is worth it.
I've done the "group of friends meet in European City" a few times... and it's always the few who fly for 18 hours and 4 flights to get to the destination that are tired for the first 2 days, whereas the others who just booked a flight and spent the extra $100 are having a great time at the destination with less jetlag.
As an aside, if you look when AC flies LHR-YOW in the summer, you can get some Star A* connections (Eurowings) | (or even via British Airways partnership) via LHR to Ottawa for not much more $$$ than a multi city connection. I.e., DUS-LHR-YOW for $50 more than/ instead of DUS-ZRH-YUL-YOW or DUS-FRA/MUC-YUL/YYZ-YOW. There is also via CDG for lots of this too.