If a good scientist says that a theory has been proved, then he's speaking informally. Mathematics deals in proof, but scientific theories are not proved. Ever.
(It is sometimes claimed that the "laws" of thermodynamics are proved. That is a partial truth. The mathematical part of the "laws" is indeed mathematically proved. The science part is not.)
The basic credo is that all scientific knowledge is tentative. Nothing is so firmly known that it cannot, in principle, be overthrown by new evidence. In practice, of course, there have been scientists who clung to old theories. Creationism, for example, hung on at many universities for decades after Darwin. The standard student joke was that evolution spread "one funeral at a time".
But belief being tentative does not mean that all theories are equal. Evidence is weighed: belief comes in gradations. For example, Roger Penrose puts theories in four categories: Superb, Useful, Tentative, and Misguided.
So, where does the Theory of Evolution fit? There are Creationist claims that scientists feel evolution is in crisis. Others say it's "just a theory", by which they mean Tentative. However, I personally testify that the scientific community rates it Superb.
Stephen Jay Gould has said that the evidence is to the point where it would be perverse to treat Common Descent differently from a fact. The most prestigious scientific journals agree, and regularly publish articles which assume that Common Descent is a fact. The Theory of Evolution is the theory they use to explain that fact.