I agree - however, there has been a strong anti-monarchy feeling here in the UK lately due to the whole Brexit disaster, so I do think that a down-to-earth (without being too invasive, of course) photo of the couple with Archie together would be a good thing IMO. I think the anti-monarchist feelings seemed to die down slightly after Charlotte's first day of school, or on social media at least, because most people with an interest were happy to see photos of the Cambridge children (especially Charlotte, who has captured most of us with her cheeky personality!).
If we weren't in the climate British society is currently in, I would normally agree 100% since we haven't seen much, as you have pointed out, of Archie's cousin Louis, and since his parents are in a more significant position succession wise, why should the Sussexes feel Archie must be seen more?