@monsterific that is in many ways why we had a fourth. And while I would never never unwish my fourth, now I've met him... In all honesty, I'd counsel any friends wanting 4 to really really think about it (or myself, if someone told me I'd have to roll the dice all over again so wouldn't get the same dcs anyway, sad thought though that is).
Ours have pretty good relationships together, DH and I do too, we earn quite well... But while they're young there's just not enough time to spend with any individual, whether child or adult. This works well for people who love being part of a pack, but if you then have a child like my DS2, who is very sensitive to the general knocks of life and other people, doesn't like big groups and needs time alone and one-on-one it's hard. Similarly, if anything goes wrong - like when my DH got very ill and for a time I was both sole earner and main carer - there's just no flex.
If I was back in my family's home country, where families live together and all help out, and domestic help is plentiful, having 4 would be amazing, but here without family or live in help 2 adults:4dcs is a hard ratio. Our DCs are amazing and we don't lack for love, money or car seats, but we have to work SO hard to make sure that there's enough time and attention to go around - lockdown has really shown us our limits.