My grandson is what one would call a picky eater and he has a major speech delay. He's been diagnosed with apraxia of speech and has sensory processing issues.
I also suggest that your son's picky eating is related to his speech delay. I urge you to get help from a pediatric occupational therapist.
You can get help thru the school districts, Early Intervention Program. A severe speech delay is considered to be a cause for concern about school success. The program is for babies birth thru 3 years old. Call you school district office for more information. The program is paid for by the Federal Government and is mandated by law.
Often a speech delay is caused by poor muscle control and/or a misfiring of nerve messages between the mouth and the brain. This can be treated and over come. I'm surprised the pediatrician didn't tell you about treatment and how to get it.
Your insurance may pay for occupational therapy if prescribed by your doctor.
This is something you need to get treatment for now. The school district program aimed up to the age of 3 has more resources available to you.
In the meantime, I would agree with giving him baby food or to mash up his food so that it's in much smaller pieces and easier to manipulate in the mouth. If his muscles are not working properly this might help.
Offer him food in small amounts. You don't need to throw a lot of food away. Put the food on his plate and let him decide whether or not to eat it. There is no way you can force him to eat. You may also be in a power struggle with him.
I urge you to let go of feeling like you have to get him to eat. I understand your frustration but it's hampering getting your child to eat. He feels the pressure and may be too tense/anxious to eat. He will not starve. Try to take a more laid back attitude. I suggest you stop looking at this as him being a picky eater but instead think of him as having a disability. There is treatment for it.
Later; Then I'd ask about adding occupational therapy. We've learned that we need to be actively advocating for further assistance. It's true that the "squeaky wheel" gets oiled.
After your SWH: Your son is at an age when it's common for them to have particular likes and dislikes. His mouth and his tastebuds are still very immature. I think you'll find with time that he will branch out. He sounds like he's better than most at finding the "offending food." This makes it hard to sneak in extra nutrition.
I wouldn't worry too much about it. I'd focus on finding out if he'll benefit from some occupational therapy that will help him eat more foods. If you make expanding his repertoire of foods an issue it will distract from the therapy.
As I recall, part of the therapy will be learning how to get more food into his like list. I urge you to get an evaluation from an OT.