How am i even supposed to fight the Grey Tempest ??

I'm just past the mid-game in the single-player campaign. This is my first serious campaign after watching a lot of tutorial videos. The Grey Storm fleets started appearing with 20k power and weren't very aggressive. But a few years later, 70k power fleets appeared and are literally ravaging all the civilizations. How am I supposed to fight this when my fleets are barely between 15k and 20k power? I don't understand how this is balanced and my my crisis multiplicator is only at 1.5x so idk why they're so strong so early.

Even when I try ship builds to counter the Mothership, I just get obliterated, and let's not even talk of the AI ​​Empires. It's so frustrating because I can't find a solution... (My crisis multiplicator is at 1.5x)
Is there any way to get rid of them without directly engaging their ships? (I know about the technique of sending ships directly into their base, but the posts about it are several years old, and I don't even know how to enter their dimension.)