Floor level can make a difference.
If the front of the bowl is higher, there will be less water in the bowl.
The red flapper lets out less water than the blue flapper.
And yes, any toilet can be plugged. They always have been able to.
That's why most homes have had plungers over the years.
A well designed toilet will reduce that, but not eliminate it.
It can depend on use too. For some reason, I've been in homes where I don't keep a plunger in the home, and can have huge parties without problems, (200 plus people)
I don't have Charmin Ultra 2-ply in the house though.
You can also hold the handle down a bit longer to drop more water.