I’m the eldest of three and I wouldn’t want it for my own children. I think two or four work better in terms of numbers of children. With three, it divides into two plus one in my experience so someone is usually left out.
Also, this might sound silly but the more kids you have, the older the older ones seem in comparison to the littlest and the more you expect of them, sometimes inappropriately. If you have a 5 year old and a 3 year old, you will expect more of the 5 year old and rightly so, but with a 5, 3 and 1 year old, suddenly that 5 year old seems quite a lot older.
I never felt I got enough time and attention. I was the eldest so was always expected to know better, to do better, and to let my youngest sibling have whatever they wanted so they didn’t kick off. I also had to share a room for most of childhood, though my parents did extend so I got my own space as a teenager.
Some of it is temperament. Temperamentally, I’d have been better suited to being an only child. It did me good in some ways to have siblings but I was always the odd one out and my parents never sought to manage that - it was my fault and I should just join in more. They were also more relaxed about everything by the time they got to the third.
As an adult, I’m glad I have siblings, though am much closer to one than to the other. But I wouldn’t have three myself.