Nice, nice, I see you did typical "whoever disagree with me is clueless" move. Very original. (Why fanboy though? You know what fanboy means, right?).
If we say "there are separate teams for next patch and expansion" we (or rather me, I won't speak for others) doesn't mean they are done completely separately. It means some people works on 10.0, some on 9.1, at this point some on 9.2, but all are on different stages of production.
I give you example: 7.3 was released on August '17 and after that they still worked on polishing Antorus (released in November). Yet when BfA Alpha came out on February, almost whole Zandalar/Kul Tiras (6 zones!) were done and questing was opened in next few weeks.
Another example: look at Anima. It's completely different as game mechanic than AP/Azerite... yet it looks similar, doesn't it? Almost like it was designed as Artifact 3.0 system (grinding Anima and unlocking Soulbind tree). Yet they already told us on SL reveal Anima won't be grind like AP. What it means? Hmmmmm.
So when I say: "I wonder if 10.0 team has same issues just like 9.1 team" I mean "I wonder if early stage of 10.0 production is delayed like 9.1, which means whole expansion is delayed and won't come in 2022 -> so 9.3 and 4th season is necessary".
Kinda obvious that if we will get 9.2, we will see Ahead of the Curve: Anduin. Last few years Blizz like to use big names for middle patches (Guldan, Kiljaeden, Jaina, Azshara, Sylvanas), cause it's hardest time to keep people playing, always launch and last patch are more popular.