Redmond and Armstrong are fine for that, they don't particularly need replacing as 1st choice. If Walcott were to rejoin it would be to replace Boufal and join Djenepo as an alternative option.
He has been in training for weeks, as shown by appearing in multiple training photo galleries and videos. What takes time is getting used to a new system, it is a risk to drop a new centre back straight into a team. Less risky with wingers/strikers.
Odds are impacted by random fans seeing rumours and putting money on it, then that snowballs as other fans see odds shortening and thinking it means something is happening even if it isn't. It really is not a good way of determining if a transfer is likely to happen.
If the source is for example Martin Semmens, he doesn't need to be told by Gao if a deal is on the cards. Gao can negotiate independently and people at the club find out at the last minute.
That didn't answer the question at the start of the post. The last time they didn't qualify for Europe just backs up my point that they are in an extremely weak league.