People keep making this suggestion assuming that putting other people on a cooldown will somehow validate them and get them slotted, it is a really bad conclusion. Making wars guild based will likely have that intended effect, but outside of that i cant really see anything added to this system to get that effect for a new player.
Cooldowns are not the right approach for getting new, or lower performing people into wars.
Guild related changes, or some sort of political system will do it.
For example if there as a larger “entity” in the game, a company of companies (we can call them alliances) and the restriction was “you and your alliance can only slot for wars”, you’d see a solution to this problem mainly. Also if we go this way it will take a long time because its a lot of work to add that system. That system should be set up to only be faction specific, so alliances can only be had internally.
I do have another suggestion that might be interesting.
That would to enable another faction to exist called “mercenaries” that could NOT claim territory but can be slotted for any factions wars (better yet if the game had some sort of “pay gold to hire” a guild type concept for that faciton).