I was one of 4 and loved it. I was never lonely, I shared a room with one of my siblings through choice (we had enough room for one each).
My mum was a teacher full time so was very busy and my parents split when I was 2 and my dad was very flaky thereafter.
But everyday my mum got us up, got us to school, picked us up from school, took us back to her school so she could carry on doing what she needed to do there, took us home, cooked a proper dinner every night, did our homework with us and read to each of us every single night. She would then carry on doing her stuff for school once we were in bed.
We had great days out in the holidays, we were never bored at home, of course some of us fought like cat and dog at times but I know for a fact siblings do that even when there is two of them.
Sometimes my mum would get run down or unwell and we'd all pitch up at my Nan and Grandad's (who had had 7 kids) and we'd stay there until my mum was better. I guess my Mum was the way she was because her mum just got on and coped with a large family.
I don't think it's specifically the number of children that are the issue more the parents themselves. If they want to make one on one time with each of their kids, they will. I was lucky to have a mum who did.
My dad's parents had 6 kids and of them, only one auntie is woe is me about her upbringing but she's one of those type of people. In fairness, my grandparents were older parents due to the war but it's interesting that only one of the 6 complains about being a large family.
I now have 4 children. They're very close in age and yes they can bicker occasionally but they absolutely love it. I haven't had any of them missing their friends all the time or wanting to FaceTime friends etc because they have company with each other. My youngest 3 see each other as best friends (they're very very close in age). Again, two of them chose to share a room, Infact they choose to sleep in the same bunk when they have one each 🤷🏼♀️
My twin girls will probably always share a room as we're very happy where we are but if they ever began to really resent it, we'd consider moving to somewhere bigger.
I guess I learned how to be a good parent (I hope) to a largish family from my Mum, who in turn learnt from her Mum and so on.