Cancelling Stargate Atlantis given the time and place was a huge mistake.
I don't think it was a good show in the limited few episodes I saw but I enjoyed Stargate Universe and thought it was phenomenal. It had a rough start but you could see the potential and it started to hit it's stride in Season 2. If SyFy and MGM had managed to keep Atlantis a little longer, it would have provided a strong lead, at least relative to the network's expectations, for SGU to find it's legs. I think a successful SGU would have opened up more exposure that the SG world could have potential for prestige Sci Fi storytelling like The Expanse.
By cancelling Atlantis, lots of hardcore SG fans abandoned SGU. Which is unfortunate as the production values, writing, acting talent and set design all took massive leaps up towards the end.
A lot of this is about timing. Vikings made on the History Channel in part because it was at the right place/right time. On another network, it would have died fast, but it held on as a flagship show for a very long time. Had SGU released near the critical praise/upswing of The Expanse, it might have been received much differently.
Bringing back Tapping and Shanks is a mistake. The only reasons to bring them back is if they still have holding contracts with the network and they will be paid anyway no matter what. This is how two Farscape refugees ended up on SG1, they were already signed to first look deals and were going to get paid anyway, so they were pushed into an existing show. Same with Tapping and Atlantis and some other show ( Haven?)
Instead of SG, Sy Fy would have been better off focusing on a Fallout series/world building. That's a universe with a built in fanbase that has lots of potential and room for growth. There would also be a wide range of merchandising potential with widespread success. If The Last Kingdom can be filmed on a shoestring budget, I don't see why a Fallout 3 storyline could not succeed with the aim towards "event television" type care and regard.
You just need to tell a good story and be willing to eat the marginal ratings. If you tell a good story, you will attract more talent, better writers and better showrunners and success can build upon itself. The basis of a good story doesn't always mean it needs to be anchored by a franchise. Krypton was actually pretty good even if it wasn't linked to Superman.