I think that access arrangements will naturally change as children get older, particularly when they start school.
For younger children short frequent visits are more important, but your dc1 is at school now and it is probably time for review.
Your ex will need to understand that he should share school responsibilities with you. There is, for example, no reason your dc1 can't go to the after school activity. However if it is on your ex's evening he will need to know this and make appropriate arrangements. Same thing if he joins beavers and it's your ex's night. He would need to drop him off/collect etc. However you can not force your ex to allow your dc1 to attend such things, he may choose to have him at home with him instead, and that is a choice he can make.
As you are both working, and dc1 is now at school, it seems reasonabke to suggest you have alternate weekends (friday to monday). So he will be having the friday overnight rather than the thursday.
It's only fair that you should get time t the weekend to yourself as he does, and the children aren't being ferried around constantly.
It also seems sensible to agree holiday arrangements now, as you are both working you will need to arrange alternative childcare on those dates you are working and have dc with you. Plus there are inset days to cover.
It is usual to have an agreement of alterate weekends (friday school pick up to monday school drop off) and half the holidays including inset days
This calculates as
39 sch weeks x 3 overnights = 117
13 hol weeks x 50% = 45.5
5 sch inset days x 50% = 3.5
This comes to 166 overnights per year which means he spends 45% of the overnights with the dc.
It does also mean that you will get a reduction of 3/7ths on any child maintenance he pays. Howeevr he will need to cover his half of the school holidays, either taking time off, roping in relatives, or paying for childcare.
You can of course adjust this as you like. ie you could continue the arrangement where the dc go to him on monday after school until 6pm.
btw you should discuss now how you intend to split the school holidays (eg alternate half terms or split them in half. Split summer holidya in two or alternate one/two week, or even ten days in a row)
Also inset days. Will you simply cover if these fall on your weekend (usually they tend to be a monday or friday - but not always), or will you alternate. And if so what will you do if there are two in a row?
It really is best to sort this out now. Are you going to put your suggestions in a letter from your sol, or suggest family mediation to discuss?
And yes a court will look at the current situation, but as your ex won't be losing time, and will in fact be gaining significant and quality time, I don't think you'd have too much trouble swappping. Unless he really isn't iterested in having the extra time with them.
he's also going to be paying less maintenance 3/7th reduction rather than 2/7ths. Course he'll have to take responsibilty for child care and arrange his holidays with work accordingly.
Have you thought about what you'll be doing for Christmas and birthdays now?