Sure is. Corbyn's gotten a lot better with his public address (although he's always been v. strong in and amongst the public) but he was hamstrung initially by having to spend an inordinate amount of time dealing with internal threats. It's a shared burden and recalcitrant MPs contributed to it undoubtedly.
I was very impressed by his set piece speeches during the campaign. I was always stumped by how bad his early speeches were. If you go back and watch his one to the Labour Conference in 2015 and watch his speech after Manchester in 2017 you can see how much he's upped his game. And fair play.