If the kid reads/solves and then behaves normally, then it is different.
2.) What you said is purely ridiculous. The "tamptrums should never happen" is wishful thinking. It is a goal to produce adult that don't throws tamptrums.
3.) Kids behavior is in fact heavily dependent on environment. Half of classroom management and child raising is literally all about that.
4.) Even many adults rage when gaming and after. Evan adults are irritable and annoyed after gaming.
I have observed, as many other parents have as well, that if the kids spend too much time in front of the screen (> 20 minutes, give or take), they become resistant, moodier, and worse behaved. This is not true if we're playing a board game or having reading time. So, I think a bit of moderation is important.
Incidentally, since having kids, I've also noticed that I am short-tempered if I spend too much time in front of the screen, a good reminder to take a walk a few times during the day.
This is not true and is extremely unrealistic thinking.
Also: some traits of your children's personality form very young, regardless of your style of parenting. Your influence is strong of course, but some things are just due to the way your kid is wired. You can set an example, and be firm about bad behavior, but some shit is going to happen anyway, tantrums included, depending on the personality of your children.
And to hell who said you get used to the smell. Second kid and I still breathe with my mouth during the diaper change.