What are his chances of a judge granting him this schedule if after 4 years, he wants 50/50?

I've been divorced for 4 years, remarried and moved on. My husband decided it’s best to stay home with kids and bring them up. Well after 4 years of me having primary joint legal custody, he wants 50/50 just during school year but not summer because he has no care afterwards. My child has ODD and ADHD and has had a structured schedule for past 4 years. I told him I have no problem with summer time for more time but not during school where he needs the structure per his school and therapist. He has shown more improvement since meds and school support. He has never taken them to doctor appointment since, has not been there for dentist etc. or my child’s cardiac doctor or a therapist. Now he feels he needs to be in after his diagnosis. Also, he has never, in the past 4 years, had them the number of overnights per the decree. Only 100/130. We went to mediation several times and all he does is yell and disrespect me and is forced to stay on topic. He hasn't given me proof of a calendar. He can even take them 130 overnight yet he wants to uproot their structure and keep them Thursday to Monday night every week and me have them 3 nights a week and full summer. He doesn't even live on the school district.