Briefly:
Partner 1 works full time with some overtime and on-call work. Loves the job but it's stressful and has a lot of responsibility so hard work. Does morning routine for toddler (breakfast, bath, getting dressed) then goes to work, 5 days a week. Is often on call or working late, but is sole earner for family.
Partner 2: wanted to be SAHP. Has lie in /personal space/chill time while P1 does morning routine, then P2 looks after toddler for rest of the day, 4 days a week. Often has to do bedtime routine alone if P1 is held up at work. Very occasionally (maybe once or twice a month) has to do morning if P1 is called in to work but then P1 will be home to do bedtime - so alternating before/after work care of toddler. Child sleeps through from 8pm until woken by P1 so no night waking to manage. Child goes to childcare one full day a week. P2 does child-related "mental load", P1 manages finances (mortgage, bills, cars, etc).
My gut tells me that if P1 is at work all day every day, that P2 should use the day the child is in childcare to do the majority of the housework (or at least what can be fit into one 7.5 hour working day (minus lunch break). P2 says that P1 is not doing their share of the housework and needs to do 50%.
Who is being unreasonable?