Firstly I'm wondering what kind of teaching your ex does that finishes at 3pm on the dot every day so she can leave and spend quality time with her kids every week day and not have any marking/prep/school events etc to attend?
If you could advise the many teachers on this forum where they can get such a job, we'd be mightily pleased. 🙄
Secondly, you seem to be denigrating every single working parent out there. Do you not realise that ALL parents feel wrung-out and stressed as they rush to the school gates, get their kids home and finish off the working day whilst the kids watch tv? Or alternatively, use after school care and have to finish work meetings on the dot so they can run out of the door to make it to pick upon time?
That doesn't make us unfit parents, it means we're doing the best we can.
But sometimes, those pick ups are where you get the download about your child's day. What made them happy, what made them sad, what homework they have etc, so when you are at home with them later you know your own child's life just that little bit better.
Yes, seeing your kids 4 days a month instead of 15 will make your life easier and less stressful. You'll have less cooking, less cleaning, zero school runs, little or no need to help with homework; you'd essentially be cherry picking all the easiest parts of parenting.
Soooooo many men do this.
And however you dress it up, it's not for the benefit of the kids, it's for you. Because you want your ex to do the heavy-lifting parts of parenting rather than you. So own it and say "I can't be arsed with this 50/50 parenting lark anymore, it's HARD. I'm going to move countries so I don't have to do it anymore."
If you can't be a proper parent, at least be honest about it.