I mean this gently, but it sounds like you have taught him that mealtimes are battles. By this I mean that YOU have expectations that don't fit an 8-month-old:
*Good eating habits are what you decide they are. (This may not be in touch with the reality of your little guy's real-life needs. A baby has a surprisingly small stomach capacity, and they have periods where they are not growing quickly and the appetite virtually disappears. This causes many, many parents unnecessary worry.)
*He will sit in his chair and should stay focused until you are done feeding him. (Kids haven't got the same needs and goals that their parents have. They know what they need, and it's movement, manipulation, play and exploration. High chairs are a recent invention in human history, convenient for moms and often hated by babies. This is not a great way to make mealtimes happy.)
*He will eat 3-4 tablespoons of food at regular mealtimes, in addition to nursing. (Not many 8-mo-old babies can or will eat this much at a sitting. Most babies do much better with more frequent but much smaller meals, and allowing them to "graze" throughout the day is healthy and natural.)
*He should eat the foods you choose for him. (It might be better to just introduce a variety of foods and let him sample and find what he likes. Protein is good, but so are fruits and vegetables, and a bit of starchy foods like rice and potatoes here and there. He's getting plenty of protein from breast milk if he nurses well, and too much protein is hard on the kidneys.)
*You can establish good table manners in a baby. (You can establish an annoying struggle in babies. They don't yet understand the concepts of right and wrong, good and bad – that comes gradually through observation. They are programmed to try to fulfill their needs. Manners will come by parents consistently modeling them, and wiggly, distracted children will eventually become civilized, delightful ones quite naturally if you don't give them too much to resist.)
If I were in your shoes, I'd take a few deep breaths, and watch what actually works. If your baby is energetic and gaining on small meals, then that's all he needs. He'll have growth spurts that will stimulate his appetite. And active days where he'll just be a little hungrier. But babies are very good at self-regulating how much food they eat against how much they actually need. Forcing him to push beyond that self-regulation tends to create eating issues later on.
If he loses weight or loses energy, get medical advice. Otherwise, I think you can safely follow his lead. Enjoy him while he's little, and let him enjoy his food experiences. He will come around as that becomes developmentally possible for him.