Comparatives may provide evidence in support of finite VP being a constituent in English, but the evidence is quite theory dependent. In her 1983 paper ‘Comparative Ellipsis: A Phrase Structure Analysis’ (which can be downloaded from her website http://www.swarthmore.edu/SocSci/Linguistics/xling12napoli.html), Donna Jo Napoli distinguishes between two types of comparatives. Belonging to the first type are comparative clauses like those in (1) (taken from Napoli (676: 4)), which can be accounted for by processes that are known to be involved in other types of sentences with missing material in them.
(1) a. Mary wrote more books than John did
b. Mary loves Fellini more than John, Bertolucci
c. John would lie to Sue sooner than Bill would to Jane
d. I organize more than I actually run her life
(1a) is an example of VP-ellipsis; (1b) of gapping; (1c) of pseudogapping; and (1d) of Right Node Raising.
To the second type of comparatives belong those that cannot be accounted for by general processes; the examples in (2) are taken from Napoli (679: 8, 9) (my representation of the missing/unpronounced material doesn’t follow her account).
(2) a. John sent books to more people than [ComparativeClause [S Sue sent books to ∅x many people]]
b. John sent books to more people than [ComparativeClause [S [NP Sue]
sent books to ∅x many
In (2a-b), ∅x many people designates the material that is obligatorily not pronounced in the comparative clause, and the striked-through portion designates material that is not pronounced but could have been pronounced. Napoli argues that the pronounced material after than must be a constituent of the embedded comparative or else form a constituent together with the material that is obligatorily unpronounced. She supports her claim by contrasting the grammatical sentences in (2) with the ungrammatical ones in (3) (again taken from Napoli (679: 8, 9)).
(3) a. * John sent books to more people than Sue sent books
to ∅x many people
b. * John sent books to more people than Sue sent
books to ∅x many people
Napoli assumes that then is a coordination word in (2), and that it may coordinate phrases belonging to categories other than the sentence, among them verb phrases; (4) is again taken from her paper:
(4) I eat more than drink
Now it seems to me that we can also find comparatives where the pronounced material following than is a finite verb followed by its direct object:
(5) He more often eats cakes to gain weight than [ComparativeVP [VP ∅x often drinks water
to gain weight]]
If we accept Napoli’s generalization, this means that the sequence finite verb + direct object must be a constituent of the comparative VP in (5), as is shown in (6).
(6) He more often eats cakes to gain weight than [ComparativeVP [VP ∅x often [VP drinks water]
to gain weight]]