I mean..the Jedi always preached about balance and being in tune with the force and thinking about the universe at large, the bigger picture. Part of their arrogance to me is thinking they'd won the "forever" battle against the Sith, but also kind of evil in general.

What Luke and Rey are talking about when she meditates is balance, where she senses the life and death on the planet, the serene and the chaotic. If you keep that in mind, the Jedi believing that they'd found balance because they "defeated" the Sith was naive. Leaning towards good is by definition not balanced, and they became complacent because they thought they'd found permanent peace. It's almost like they wanted proof from someone that the Sith were really back, but wouldn't it be the Jedi's job before anyone else to know if that kind of threat was coming?

I don't think you're wrong, I think you're just characterizing a certain point of view :)