Oh, that's right! The Arrowverse did tease that they were doing a Crisis on Infinite Earths crossover next / this coming winter. And in the last crossover of Elseworlds, Oliver clearly made some kind of negotiation to save Barry and Kara with the Monitor. I wonder if that will tie into the end of Arrow. Perhaps Oliver will die at the end taking the place of Barry and Kara who died in the comic original Crisis.
As for your point about these shows ending and transitioning / setting up other series, that might be happening here. CW is apparently moving ahead with a Batwoman series after the debut of the character in the Elseworlds crossover. Rumour currently is that this new Batwoman show may be taking the place of Arrow.
As for Arrow being past time, I disagree. Yes, season 6 ended up being a bit of a disaster although I feel it was able to salvage itself a bit near the end of the season. And I've been enjoying this current season so far. It's definitely rebounded from that season 6 although I think all the Arrowverse shows are having a bit of a rebound season this year aside from LoT which was easily the best of the bunch last year. Unfortunately, the writers did hurt things with some of the decisions made and how they used the cast which has required some twisted logic and dubious character motivations along the way to create certain situations or fixes. Yet, there's always been some well done moments to appreciate over the poorly done and it's managed to keep me still watching up to this point. I'd say Legends of Tomorrow is the best cast right now but of the remaining Arrow shows, I still find the Arrow cast to be the second best overall and ahead of Supergirl and The Flash's cast. During the summer, I was thinking in my head what I would do to fix Arrow if I was the showrunner. I might share a bit of the idea yet one of these days but I saw a path to make the show last up to a tenth season with possibly an eleventh season for a longer send-off. I even thought about it as a shortened season so it is weird to see season 8 announced as a shortened season. Still, I guess what this long paragraph is about is that I'd actually rather see Arrow stick around. Heck, if I was cutting one show, I think I'd pick The Flash right now over Arrow but I might be the only one to feel that way.