Is the difference of opinion among mujtahids an inconvenience?

No, on the contrary, those differences brought about mercy and ease for the ummah.

When people faced difficulty regarding an issue in a madhhab, they coped with that difficulty through an easier judgment of a different madhhab when there was real necessity. Thus, the existence of madhhabs enabled ease for the ummah.

Probably, that must be the meaning of the following hadith: “The difference of opinion in my ummah is mercy.”