It had that feel to it, like everything was tied up and the story has nowhere else to go.
Possibly. That is a risk for the show though as people's tastes change and a break that long will have people forget and lose interest in the show. Not to mention if they do give it a go in 2022 a lot of people who aren't already at that stage might watch it and think "wow, this is really bad, I can't believe I used to watch this crap".
The writing is terrible and far too convenient. What happened? I think in part they ran out of things to do with Shawn. A lot of shows have this problem, in reality Shawn (or in general a character) needs to progress even if they don't realize it. But with TV the whole point is that they are challenged in some way, so they can't progress like someone would in reality. So there will always be inconsistencies.
The Carly/Shawn thing was terrible from the start. They lacked chemistry and given that Carly looks a lot older than Shawn it had a mother/son feel to it at times which increased the discomfort level. I just looked up their ages and Jasika is 11 years older than Freddie.
Carly then continuing to be very insecure about Leah was weird and seemed out of step for her character as well. It was like she just wanted out and so did the writers. Of course it was all designed to lead to Leah and Shawn being together. Overall way too easy.
In terms of Autism, I still wouldn't Shawn anywhere near me if I was ill. That thousand yard stare of his is just weird.