Off topic question: I noticed that empire was equivalent in strength to you, and you yourself are pretty sized up,. Has the AI gotten a beef recently?
I'm playing on Grand Admiral difficulty with 1.25 habitable worlds and 2x hyperlane density. Hyperlanes at 2x is ideal, because otherwise empires have a hard time expanding due to how linear traveling becomes but still allows you to have some chokepoints.
Higher habitable worlds means they can expand to more planets and produce more resources which produces more ships which the AI is very good at due to the bonus to resources they get. Anything higher than 1.5 habitable worlds seems to cause lag even on medium sized maps, I sent it to 1.25 due to me planning on playing this game out in full, perhaps to the year 2900.
I'm also playing on the 2.2.3 beta which fixes a lot of things, though there are still some stupid things the AI does, machine empires building farms for example. Grand Admiral in 2.2.3 is easier than Admiral in 2.1, but a way with that empire's federation would be difficult, even with my abundant alloy income.