For some reason Boeing made the 777/787 slightly too wide for 9/8 abreast so of course eventually the airlines realized they could snug in another column of seats. The airbuses generally don’t have that problem because they are already quite snug in default configuration. So ironically a product less comfortable by design ended up being more comfortable.

10 abreast in a350 sounds terrible though. Might work for shorter ultra cheap charters but I very much doubt that any mainline carrier would consider it. Think they did a similar concept with 11-abreast a380 but luckily no-one caught on.