Discussed many times already.
While I basically agree, don’t forget that this would make it much harder for 10min startups to enter the market. Yes I know, the experienced player…
But you need to set up a game for the average player.
Airport fees already, in a way, force you towards flying to smaller airports, at least if you want to go for higher profits. Since larger demand airport combinations cost a higher fee. For example, AMS-LHR is much more expensive than AMS-LTN (for an A220-300 it’s $2,457 vs $931).
Speaking for Europe at least, free slots do NOT cost money. Slots are allocated at a twice yearly slot conference, and only if you want to trade slots with another airline, they cost money, whichever price the other airline demands.
So once again, slots given out by the national regulative authorities (e.g. in Germany that would be the FluKo - Flughafenkoordination, which translates to airport coordinator) don’t cost a single penny.
In reality, slots don’t cost money at all, for 99% of the airports in the primary market (that is, between the airport and the airline). Few airports have tried auctioning its slots (one example was CAN back in 2015, but failed) but the vast majority follows either the first-come-first-served rule, or a pre-defined administrative allocation rule. LHR falls into the latter category.
The price you see on the news are from secondary market (that is, between airlines). This will only happen in airports where slots are extremely scarce. Some regulators specifically prohibit selling/buying slots, but only allows trading slots with slots; in other words, cash cannot be involved in the transaction.
In the notable case of LHR, you can very well tell that airlines selling the slots are those with long history of presence in LHR who easily got the slots decades ago. They are basically making money out of nowhere. If you put such feature in a game, it would be death sentence to new players.