That and I could see some countries getting 2 or more airports as they are very diverse. Sadly LHR is the only airport in the UK that’s limited on traffic types whereas MAN could happily fill that hole, plus if the devs are generous and happy to bend all that timey wimey stuff, BA had their base at MAN until the mid 2000s with the likes of BA Connect based there but also the 757s and 767s they used to do routes from with. It would allow for all options rather than the limited scope of LHR.
In regards to the other countries I could easily see another Italian airport, most likely in the North with Malpensa or Linate or even Turin, or maybe a third in Sardinia with Cagliari. Spain could have 4 with PMI, somewhere like Malaga, Seville or Valencia, a northern airport like Santander, Bilbao or Asturias and then a Canary Island one, maybe more. Germany the same, I think Hamburg and Dusseldorf are good shouts for 2 airports with a good amount of distance, which are interesting and not too big like Frankfurt. France could also do 2 airports like Bordeaux and Paris or Lyon or Nice which are all nicely sized (Except CDG which is huge lol).
USA could do with more airports I agree, I’d personally love to see Minneapolis, but the advantage Europe has I think above most places in the globe is just how different the continent is over small distances and that’s reflected in the airports and airlines/liveries which I think are what bring a lot of players into the game. Plus having Manchester doesn’t limit the likes of Edinburgh or Dublin to come to the game as again there’s enough distance.Big hubs are fantastic if you want 300 A380s in your livery but the smaller airports have a lot of character and allow for these different airports to exist, plus those who like their own airlines can run their own little regional fleets which is a lot more realistic.
Canada deserves an airport though, whether that’s Calgary, Montreal or Vancouver (Though the latter would be good when seaplanes are added).