Can please someone link this crucial information to the devs about Elo:
Elo is a logarithmic projection of the strength distribution. That means, that if you want to add elos, you have to use the correct addition method for logarithmic functions.
How this works is described here .
And how you can practically implement is described here.
The basic concept was proposed by @Mercy9545 years ago here
Every attempt to add up elos in different ways like just directly adding them up is doomed. It won’t work, cause it ignores the basic mathematical properties of the elo system.