Churchill was not involved in the execution of the plans at the Dardanelles. The British drew short straws in the on the spot leadership in both the Naval and Military departments. De Robeck and Ian Hamilton were both remarkably good at missing opportunities.
And there is the matter of extreme bad luck, which haunted the Naval assault especially.
Hamilton wasn’t given the troops that he needed (and asked for) and didn’t have adequate air support, particularly in the early phases.
Of course Churchill wasn’t involved in the execution at the operational level, but he was fully involved in the conceptual aspect and approval of it, and in conception, it was a very, very bad concept.
The failure of that should have rested squarely on his shoulders. That he was able to resurrect his career later on is a tribute to him.
There was a very high degree of contempt (and rightfully so in some aspects) for “The Sick Man of Europe”, but to base the entire success on the plan on the judgement that they would just fold on their own land was beyond stupid.