I have said time and again that buying planes to lease them out is to absolutely _NOBODYS_ detriment, especially not smaller players!
Of course it's to the detriment of smaller players.
There is a cap on new plane delivery rate, in an attempt to ensure that all those who want to get a particular plane can actually do so.
Large airlines circumvent that cap by having others acquire planes for them. Other large airlines try to be airplane retailers, buying new wholesale planes and then selling at a markup, something that no RL airline does. Both those things mean that some production lines get very full, very fast, and smaller players have no way to get those planes other than an extremely long wait or by paying a big retail markup from one of the player-brokers. Which is clearly to those smaller player's detriment.
The cap on new plane deliveries cleary isn't doing the job it is supposed to. On some unpopular lines, players can't get planes at a practical rate. On very popular lines, smaller players are quickly locked out by bigger players circumventing the restrictions.
You could just have unlimited production, as Jumboshrimp suggests. You'd remove the incentive for players to go into the airplane retail business themselves, you'd no longer leave small players locked out. But you'd still have the problem of players circumventing the delivery cap, that instead of getting 2 planes/month delivered from one line, they could get 8 planes/month delivered by also taking the quota of 3 friends via the UM.
You'd also remove the need for players to make tougher choices about which plane type to fly, to weigh up availability vs operating costs, etc. No reason to order new MDs when everyone can get new 737/a320.
I don't think having airlines also trying to operate as a new plane retailer is a good thing. I don't think airlines being able to use their friends to circumvent restrictions and reduce supply for everyone else is a good thing. I find it weird that people who like to get very hung up on what happens in RL in other areas don't see how different to RL this area is. And I'll still do both of them myself, because they're both very helpful things the way the game is currently set up.
From a gameplay perspective, I think it'd be much better if that nominal cap on delivery rate for new planes actually applied to all airlines, if they couldn't work around it the way they currently can. It would mean that for rapid growth, to end up with any sort of huge airline, you'd need to run more than 3 fleets. So it'd also mean drastically redoing the fleet commonality system, to remove the absurd penalties for running more than 3 fleets we currently have.
Plane launches, and assigning delivery slots could be done much better, much more fairly, easily allowing everybody who can afford it to get new planes at a reasonable delivery rate and waiting period, thus removing the incentive for player-retailers/brokers. Unpopular lines could actually be acquired more quickly if you could afford it. I'd stop players having the ability to circumvent delivery rate restrictions, by making changes to the UM, also making that fairer and less of a lottery. Would also reduce the opportunities for cheating by transferring cash. Would no longer be possible to get 100+ planes of the same popular fleet in a year, so would also mean changes to commonality. End result I think would be a fairer, more competitive, more challenging game than what we've got currently.
I'd much rather have building a huge airline be a challenge, instead of being very easy as it currently is. That airline success came from building your airline well, making good choices, rather than so much of it being from how well you can circumvent ingame restrictions by using your friends to get extra departure slots, extra production slots, extra cash. That players had choices to make, instead of always being pushed towards doing the exact same thing to get a large airline.