I have been thinking about this a bit. Right now there is not really a way to spread the load out like you mentioned. Anyone can make another instance, but it doesn’t really alleviate any of the stress from another instance. I think it might even add to it, although not as much as adding a bunch of new users would. It would be beneficial to be able to contribute compute power to an instance, but I don’t think that is a realistic goal with the way Lemmy is setup.
My wording was poor. I ment that currently there is no way to contribute to reducing stress on an instance. Making your own instance might help prevent the problem from getting worse, but it is not the same as adding more cpu power or ram to an instance. If a instance is maxing out on it’s CPU power, currently there is no way to allow other people to help disperse the current load.
On a slightly tangential point, I am not sure how sustainable it is to increase the number of possible users by increasing the number of instances. It is already a frustrating process finding the right instance to join. So imagine when there is 1 instance for every 100 users. With 100k users that is 1000 different instances to sort through. I think there needs to be better ways to scale Lemmy, especially the amount processing power it requires. Lemmy.ml will only be able to scale so big on a single vps instance, or even physical server.