A few random thoughts for you -
There is more to a preschool than a name brand and a philosophy - what is labelled Montessori at one school might look very different at another school. School staff and their interpretation of school philosophy as well as their way of working with children all make a huge difference in a preschool experience. And all children are different too. Some children like to be shown how to do things, some children like to be creative, some children like structure, some don't... etc etc etc.
This is really neither here nor there, but fwiw, my ds wore a top-knot 24 hours a day from the ages of 2 1/2 - almost 4. This included spending a lot of time wearing his top knot at his Montessori pre-school

The top knot was his choice, not mine. No one cared at his pre-school. They also didn't seem to mind that he rhymed. CONSTANTLY. The preschool teachers just seemed to love him, and they seemed to love *all* the kids at the school. He's 13 now and I kinda miss the top-knot rhyming years
It sounds like you don't have a good fit for your ds at his current preschool. So I'd try to change him to a different school. You mentioned your only other option is homeschooling - is that really the only other option? I'm not saying homeschooling would be a bad choice - it could be a wonderful choice! Just wondering if there really are no other options where you live and why no other options for preschool?
Last random thought - don't stress over whether or not you find out your ds is profoundly gifted, a little bit gifted, or not gifted at all through the testing. Lots of parents (seriously!) ask for gifted testing before their children enter kindergarten. Some of them will find out their kids aren't gifted. It doesn't mean your ds is any less amazing, magnificent, wonderful and it doesn't meant that he won't grow up to change the world or be successful or any of that. It's just a number - actually a set of numbers - and whatever the magnitude of the numbers, they can give you some great, interesting information about how your child learns. You have a chance to get those numbers for free from the school district so go for it! Chances are it's unlikely you'll ever see the same tester again either... so don't worry about whether or not you've overthought anything or asked for something that you didn't need to or whatever. Get the testing done, ask questions if you don't understand the results... and in the meantime, try to find another option for preschool. No matter what the level of giftedness or not... it sounds like your ds isn't happy where he's at, and it sounds like the staff is more rigid than your personality. The preschool years go by to quickly and our kids are very impressionable at that age - you and your ds will both most likely be happier somewhere else.
Best wishes,
polarbear