Most claims that include the words “better”, “best”, or “worst”, are difficult — if not impossible — to prove right or wrong. To confirm without subjectivity, comments must be tested empirically, or at least be backed by empirical evidence. (DC Theater Arts)
In terms of the quality of the film in comparison to the musical, there are only a few numerical values that we can predicate the response on, the most obvious being profit.
Wicked — the movie adaptation — has made approximately $756 million worldwide at the time of writing this. In comparison, the musical’s profit reportedly surpassed $1 billion in 2016. It is also important to note that the musical had a 22 year head-start — at this rate, it is safe to say that the movie’s profits will surpass the musical’s. (Box Office Mojo, Wikipedia)
Most, if not all, other elements of the movie are subjective and cannot be factored in when deciding the merit of the film.