lol even deadpool had ryan reynolds.
How much do you think Reynolds cost the studio to cast in Deadpool? At that point in his career, he was actually box office poison and anything but a draw. Before Deadpool he was attached to Self/Less, Criminal, The Voices, Woman in Gold, RIPD, Mississippi Grind, and other movies I've never heard of because his status wasn't "A-lister." Just because people knew who he was didn't mean he was an A-lister (people know who Nicholas Cage and John Cusack are too). Let's call it like it is: Deadpool resurrected his career from the cheap and/or direct to redbox stuff.
Yes, Reynolds brought an incredible amount to the Deadpool project, but it wasn't his name that made the difference - it was his dedication, humor, style, and talent behind an anomaly of a film that had great word of mouth and an excellent marketing campaign with essentially no real competition at the beginning of the year.
This is does make me worried about the script though. That is if these actors declined because of that.
Though it's possible, I doubt Shane Black gave the thumbs up to a script that actors don't like. Especially in a world where 2016's X-MEN Apocalypse, Collateral Beauty, Assassin's Creed, Suicide Squad, Huntsman: Winters War, Allied, Gold, Sleepless, and BvS attained many or a few A-listers with their garbage scripts. Maybe a few big names didn't like the script itself, but I imagine the script isn't the problem.