This one is going to anger Russophiles in a big way. A state aligned paper published an article stating the Russian space program is rotting within - that's literally the title of the article - and on the verge of a catastrophic collapse:
MK is formerly as Moscovsky Komsomolets. This paper has been around for a loooong time and was even an official publication during the Soviet Union. I've not heard of the author before. I do not know what, if any, axes he or the paper or its backers have to grind. That said, the article is pretty damning.
For those who do not read Russian or wish to rely on Google Translate, Ars Technica has a write up and at least some of a translation.
Soyuz can haul all of 3 passengers.
Dragon manned can haul 7 passengers at once.
The aim of ISS program management is to get as much done as possible. In the long (longer than should have been) period after the Shuttle was retired and NASA was reliant on Soyuz you had a max of 9 occupants on ISS for short periods. Due to lack of an escape system if an astronaut needed to return to earth due to health all 3 members of a Soyuz flight have to leave at once.
Once Crewed Dragon started flying you get up to 12 ISS occupants. Mixing an American into the Soyuz flights was so that the International segment had at least one person to maintain operations. generally though they keep it at 7 with 4 from Dragon and 3 from a Soyuz.
Despite the name reality is that their is a boarder on ISS. The Russians tend to the Russian segment the Americans tend to the International. They do get together but both agencies really run them separately. As such with Dragon’s ability to haul larger crews means that the ISS International segment is more likely to be crewed than Russian. But the same rules apply. If you have an emergency needing to cause astronauts to return to earth having a Russian in the mix means that the Russian segment has someone to operate till the next Soyuz. So mixing is a good idea. Having some NASA and Roscosmos on each other’s craft is logic.
Soyuz is already as efficient as it can be in terms of size without going to a larger launcher. That is why the Russians are developing the Angara A5. That should have enough performance for a larger capsule.
Well as efficient as a design dates from the 1960s can get. I mean it’s a 2.5 meter capsule directly evolved from Vostok series riding on a ICBM.
Dagon is a 9 meter capsule that was started from scratch to be a modern space Taxi.