How about if you view it as an 'activity' rather than a 'meal'? If he is interested in your food and wants to hold a piece or smoosh it around his tray he is still learning about food, the smell, texture, temperature, smoosh-ability (so quite a lot really) he is also learning about the social aspect of coming together as a family for meals, watching you use cutlery, seeing how you make conversation as part of the time spent together etc. He is getting some fine motor activity when he squooshes and smooshes the food, picking up finger food is great fine-motor practice and pincer grasp practice, even drawing/mark-making with his fingers in dip or puree are the very first 'practices' for drawing and writing much later on.
In that sense none of this is a waste of time although I can understand the frustration for you if you are preparing meals for him and feel like lots is going to waste.
If it was me I would probably continue to bring him to the table for meals times, let him down when he shows he's had enough sitting (not expecting him to stay the full meal like you would the other kids), and just offer 1 or 2 little bits of something you are already preparing so it isn't additional work (just throw in an extra bit of veg when you cook). I don't have other children but I imagine it could be handy to have your 6 month old join you all at the table at meal times just to have somewhere to put him for a short while, whilst you get to eat your own dinner.
It's also fine if you want to stop for a week or two though!
