So the only other 4X space game I've played is Stellaris, and in that game even the small map is massive with 600 systems. But when I jump into ES2 it feels so small and everything being connected to hyperlanes makes it feel even smaller.

How long does a match last on the default galaxy map with the game pace being quick? It just seems from size and stuff that it's like, 5 hours haha. I know it's not but average length?

Frankly, it's Stellaris that's the odd duck out in space 4X games. Space 4X classic Master of Orion 2 has a map that's only this big:

While the more recent Galactic Civilizations 2 has a map like this:

(Each cluster is a single star and its surrounding planets, if I'm reading the key properly.)

Plus Stellaris's systems usually have just 1 or 2 inhabitable planets (if any at all), and its uninhabitable systems just act as rest stops and locations for mining stations. Meanwhile each of Endless Space 2's systems have 2-5 inhabitable planets, so it's not quite as small in comparison.

And personally, I would rather take 5-hour matches than the 15+ hour matches most Stellaris games turn into.