Review response to quite positive review comments - first grant I recently received the review reports for my first grant. All four scores were 5 out of 6. The comments are also mostly positive. Two criticised a bit about the pathways to impact and the support from the department, but nothing major. 

What do you think I should write in my response? I've drafted a version and made a response to each point raised by the reviewers. However, my mentor thinks that probably the reviewers were not enthusiastic enough or something like that - and that’s the really serious thing, and that I need to emphasise my proposal is great, not to answer the "lazy" questions from reviewers. 

I am a bit confused. What shall I write then?
I assume your question is about one of the UK Research Councils, probably EPSRC. If that's true, then 5555 is currently considered quite a low score, and such a proposal is not likely to be put forward for funding during the Panel meeting (unless you have a year with unusually low competition level, or someone in Panel is really keen to fund your research). In fact, the competition levels in EPSRC right now are so insane, that even proposals scored 6666 are not always supported. 

The fact that you have "lazy" comments from Reviewers makes your situation even more difficult, as you are not given a good chance to stand for yourself by answering the questions. Your mentor is right that at this stage you have to write a really brilliant Response to Reviewers to make your proposal fundable. 
Good luck with it.