I think that doing a little bit of maths every day can be hugely beneficial. For most children, there is not enough practice at school, they learn a concept but don't get a chance to really 'master' it before moving on, instead they re-visit the concept a few weeks/months later, when again they don't get enough chance to practise.
The way I see it, Kumon can in some cases give you this extra practice, and you as a parent don't have to worry about planning/deciding on content etc.
But it is an expensive way of achieving this, and doesn't seem to be working for your child. And as you say, no 'challenge/lateral thinking' - no, I do believe Kumon is not designed for this at all. More for just practising the basic concepts and techniques until they are completely fluent.
You could look at online programmes/apps instead, perhaps? They can be more engaging. You could combine some that provide practice, with some that are more problem solving focused. Also you as a parent have the possibility of changing the level the child is working at, rather than just following the Kumon tutor's advice, if you feel it is too hard/easy/boring. Of course, that in turn requires you to put some thought into it and engage with it more than you have to if you completely outsource it to e.g. Kumon.
That said, you mention your Y2 child is doing column addition, doing well at it presumably? At our school they only introduced column addition in Y3, quite recently actually. It is not part of Y2 curriculum. Your child should not be 'behind' because of column addition. Is the problem more that he struggles with more basic things, which Kumon have ignored, and instead drilled him with stuff he isn't even expected to know yet? So he has been practising column addition for a year now, you say, but hasn't practised the stuff he ought to have been practising, the Y2 curriculum stuff?