I mean, if they were the isolationist we know them as then the slave camp wouldn't be possible, and when the UP set up shop there during the Mongul arc they comment on how it's a "fixer upper" because it's a lifeless rock.
Now technically that does everything short of outright saying they're not a thing (however you can organically say something has never been a thing), but still, the intent seems clear. If someone wants to come along and use what I've always found to be frustratingly not-Kryptonians while PKJ's new race and Zod's New Krypton are around, well, that's...fine.
Like, Zod's young New Krypton could easily be isolationist, and that would do more to serve the Superman world (and Zod's character) and overall DCU than any use of a race of Supermen allergic to pencil led.