The EP sounds sympathetic and possibly informed if they are making astute observations that you agree with.
See if you can get the EP to help you explore options with the school and LA.
I'd suggest you ask LA to provide PDA-specific alternative provision for half a day via a specialist provider at home, and half day in school.
Providers who understand PDA are SenSe Learning and Wildheart Foundation. They have trained tutors and learning assistants who come to your home and do learning through play, low demand stuff.
Don't try and "teach" him yourself, it will kill you dead and it may push him towards entrenched avoidance around learning.
Pedal in the opposite direction. No/low demands. Follow his lead, and go with whatever his own interests are. Hold things lightly, learn how not to push, how to acknowledge and let go of your own (perfectly natural) desire for him to be "educated".
I hear you about missing your older child. Please know that parenting a PDAer can get easier when you find what works. You might have to turn your household and expectations on their head, and life won't look how you planned, but I promise you life for the whole family will be better when you find what works. It will be ok.