I do know the area. It was my local route (I proudly had an NN7 postcode and had the awful Andrea Leadsom as my MP). The 7's only run every 30 mins so the diversion of the X4/X7 means they have an important role in serving Grange Park and especially providing a faster link than being dragged all round Wootton. Also, the diversion around Grange Park is also important in providing a link from there to Milton Keynes which, to the uninitiated, is quite popular for Northamptonians (given how lousy the town's own shopping is - not to be helped by M&S closing there). Therefore, whilst there are alternatives in the 7, these are not good alternatives.
On the northern edge of town, I know what you mean about the number of services running via Kingsthorpe. Again, you do get passengers from there to CMK (amazing, I know) but also it serves the top bit towards Boughton where, incidentally, a lot of new housing is springing up.
Granted, from Kibworth Harcourt into Leicester, or from Roade into CMK, then yes the X7 is very much a happy bounce along the A508. However, this is the danger of merely looking at a map - there's more to it than meets the eye.
Personally, I'd not be surprised to see it get converted to Gold standard with e200mmc so that there's some commonality with the X4 from Northampton to CMK. That said, I'd expected that some time ago and it still hasn't happened
Instead, they converted the X46/X47 rather oddly