No, these are two independent clauses:
Toibin and Catton hardly read Crace (or Shakespeare, Austen or Dickens).
Toibin and Catton feel that the riches of English are "his before they are mine".
The author feels that both statements are worth mentioning, but the author does not feel there is a direct causal relation between the two. If it would have been there, he would have used thus instead of and if what they feel follows from the fact they hardly read, or he would have use but if he wants top emphasize that one would expect them not to feel this way.
However, he simply states they hardly read Shakespeare, and also, unrelated as such, the feel something.
The sentence is not different in build up from this simple example:
I got up this morning and ate breakfast.
Two things, both happened to me, no direct relation.
I got up very late this morning but still ate breakfast.
Getting up late may imply I have no time to eat breakfast but contrary to that expectation, I actually did have breakfast.
Using but instead of and as you propose would change the meaning of the sentence considerably, and I would assume that if the author intended the sentence to have another meaning he would have written it differently.