To me that sentence you quote sounds like mild praise, "practise not so bad" within that sentence construction implies not that his was only half-way terrible but that it's a pleasing way of comparing him as it incompasses a sort of rhythym in the sentence - point and counter-point.

There is some evidence in the book that the parenting isn't left up to the nursemaids as totally as it appears to have been in some Victorian households I read about. We are told in chapter 5 that the furniture in the drawing-room is "growing shabby under the influence of four summers and two children", and Mary has had her boys with her that morning. The boys have been off at Great House often enough for Mrs Musgrove and Mary to both have their complaints about the situation, and they're in the middle of things when the Croft visits (he spends all his visit taking notice of them). I am not sure how the quality of this contact counts in terms of parenting, but they do not appear to be turned over to the nursemaids and seen but never heard.