I was also confused why Alfie crossed the Shelbys. He seemed to be aware that Changretta was the bad guy ‘you’ll kill us all' but bowed to him anyway. I guess he was just resigned to the Americans winning 'big fucks small' and assumed the magic eoukd beat the shelbys.
IIRC series 4&5 were commissioned together. I think the writing for both has overlapped and the speedy series of events in the last 15 mins was just clunky set up for next season.
I also found the seduction of Jessie Eden jarring.