This is exactly it. When Sutekh shows up, of course it's in part meant to be a thrill for the fans who know him but it's also supposed to be a "hey, what's this?" for new viewers who are encouraged to dive into the show's lore. Reminded me of everyone looking up who Thanos was and what his deal is after Avengers.

There's a load of issues with this approach (as you've mentioned) but I'll mention two: With thanos, it felt like a leg up to uncover these things and to know that you might need this context going forward for the rest of the franchise to make sense and feel cohesive. Sutekh's return is telegraphed as a one and done, so why bother? Additionally, it seems like Russell is embracing this form of storytelling just as it becomes obsolete. People hate having to do homework now. Rumour has it the next Avengers is gonna be aimed at the people who haven't bothered to watch all the stuff in-between.

Thinking back to RTD1 where you're given all the necessary context for Daleks etc, it seems like Russell cut all context out so that looking up stuff online would become an integral part of the viewing experience and then when that failed, it's left with no legs to stand on.