If anybody comes to this, i will answer the question how it was solved.

Because iteration (#each loop) of the pages happens after the summary page in terms of lifecycle, the actual pages are put at the end.

In the actual code, i was getting an error which lead me to wrong conclusion that the each didnt render the pages. It actually did, but the wizard navigation didnt work because of the yet another form issue.

In any case, example in the REPL works fine, but still, i couldnt fix it that the order is kept (first pages coming from api, then the page manually added after them). #key directive didnt help