To play Devil's advocate here...
If they made a shared universe with a different style tone and formula than Avengers, it might work well. Almost every Robin Hood movie has the same beats, because Hollywood is notoriously afraid of risks; even Scott's grim and gritty version was created with the three act structure, train the villagers, win the girl at the very end story in mind. But, and this is an idea for a book series I might try and write some day, what if Robin Hood was in each film, but with limited but awesome screen time, while Tuck, Marian, John and Guy were the main focal characters and protagonists?
The original script for Scott's version was 'Nottingham' and the idea was to have Robin as an antagonistic thief the law abiding Sheriff must content with during his investigation. I read the script and you know what? I thought they could have gotten a huge amount of mileage out of shifting from their very deconstructive version of Robin (run of the mill egotist and robber) into a more sinister trickster archetype. Just imagine a movie where Robin appears only three times, but once or twice in disguise good enough you don't know it's him, and the third time with a big and disconcerting Cheshire Cat grin on his face.
I like the idea of Guy of Gisbourne competing with Robin as outlaws, or of the Sheriff facing the realization that he has zero control of his shire outside his town walls, or of Marian learning about and fighting the more mysterious Hood to meet the guy inside, or John being inspired by a genuinely scary rebel.
The only indisputable advantage of a shared universe is that it's built for sequels, so something like the idea above could make it a very nice series.