This is despite Gayle have done more with the bat and in the field to push Australia than any of those guys. And, in the first Test, even with a great ton from Barath, with no score from Gayle, they got smashed. Next two Tests, Gayle fires, WI push the Aussies to day 5 in both. It's no coincidence.
Point is, Gayle is the biggest predictor of WI success right now. Whether he has decent back-up or not, if he fires, the WI do well and when he doesn't, they don't. That he's had a run of outs in the ODI series doesn't mean he's suddenly turned to crap, provides no leadership, etc. His lack of form is a reason for the WI lack of success, not his fault alone. It's a guess but I'd suggest if the selectors went temporarily insane and dropped him, the WI would do far, far worse.