I think it's behavior related. He is a very strong willed little boy.
In that case I really think an OT can help. They have such amazing tricks. It would have to be one specialized in feeding therapy though.
from my own personal experience: offer often, in various settings. For a 'normal' kid with no food issues, it can take up to 20 times of offering a food before they accept it. So it could be much more for your DS. My DS was so cautious for a long while. He just recently started to be more open towards new foods. Don't be stressed, try to be as easygoing as you can. Give very soft food because it is easier to chew and since he has not eaten a lot in his life yet, he will need to practice because he can master chewing harder foods (for example one of M's safe foods was green beans, the OT made us give him canned green beans to help him practice since it is really soft and now he's onto just regular cooked green beans - the canned ones were just for a transition, they are pretty much void of nutrition but the goal was really just to get him to eat them). Really just offer, offer, offer. Our issue is breakfast and M is not eating a few cereals standing on a stool with his bowl on the big table. He loves it. It'snot ideal and it makes a mess sometimes, but at least he eats a little bit.
I've also noticed both my kids always eat much better at daycare than at home. I think it has to do with distraction, and also seeing every other LO eat too.
As for reflux meds, this may be unconventionnal, but although I can say that M absolutely needed them as a baby, he did much better once I weaned them at 10 months. He started eating better shortly thereafter. Reflux meds make the stomach less acidic which can make digestion more difficult. So if there is reflux of course they may be needed, but if he doesn't have reflux, the meds can actually cause some trouble for him. Just a thought. However if he has been worse since you weaned the AM dose, then probably reflux is bothering him
FX he likes the smoothies!