I think the problem highlighted by OP is that we don't have proper data on homework.

At best, the stats you share show that 'it is possible to deliver the best global educational outcomes without giving children homework'.

We don't have proper data on whether these educational outcomes could be further improved by assigning more homework.

I think Finland is not a particularly helpful example to share here, specifically because they're widely lauded for having an excellent educational system across the board, they could quite easily still be world-leading even if they've got it wrong on homework (although I accept it probably means that the best education researchers have likely considered the homework question in Finland and have come to a position on it).

From a personal perspective, I think there are a lot of factors to whether homework is useful.

For example, in a former life I was a languages teacher, and I saw the children I worked with for one or two hours a week. In order to learn vocabulary, without a doubt the most effective method I've ever used is spaced repetition. My best chance of teaching vocab items is to open the lesson by introducing them, a mini-recap at the end of the lesson (maybe a memory quiz, etc.) and then for the children to review themselves at some point before the next lesson. I would imagine similar techniques would be useful in most subjects.

Anecdotally, I saw faster and more secure progress from those children who had done the homework.

Additionally, those children who had done the homework tended to be better behaved, more responsive to 'course-correcting' when they got distracted, and were able to exhibit better self-control... obviously all of this carries a heavy caveat that this may be WHY they were more compliant with the homework, rather than a consequence of it.

However, with a bit of common sense (and to be clear, I have not searched for evidence for the below, and it may well not exist), it seems to me:

1. There are some things where short stints of 'self-learning' are clearly beneficial, and it is either not possible or not an effective use of time to do this during teacher-led lessons (eg: vocabulary/rote learning, independent reading of literature, etc.).

2. A requirement to do some task which does not lead to immediate gratification builds a habit of doing things that are not necessarily fun just because they need to be done

3. Learning to be able to self-manage and complete tasks by a deadline is a skill to develop on its own

4. Learning how to cope with not having completed a task just before the deadline is also an important skill ('can I get away with very quickly doing this in the break before the lesson? can I copy from someone else? should I admit to the teacher that I haven't done it? should I make up an excuse?' etc.) - as long as it's relatively rare

5. Excessive amounts of homework which interfere with a child's private life/free time/etc. are unlikely to be helpful - between 0-5 hours a week total across all subjects seems like a fair amount.

6. Schools should take care to co-ordinate homework so that it's balanced throughout the week (eg: giving 3 hours of homework to be completed on Monday night and none for the rest of the week is not sensible).

7. Teachers should not use homework as an excuse for not planning time properly in a lesson ('oh we're out of time, please finish this at home')

NB: Edited for formatting.