I have seen people being asked to take off their boots at Toronto Pearson.

That's because US bound flights have separate security, which operates with different standards.

Nope. This was for within Canada flights. Its also only for people wearing large boots in the winter.

This is a regular occurrence in European airports.

No it's not. I fly regularly intra-EU and maybe once (?) have had to take my shoes off in the last 5+yrs....can't even remember. I don't know which airports you transit/use but I go throw most of the major ones across EU pretty regularly.

All major ones.

Usually I see it happening to those lucky ones carrying boots or shoes with thick sole.

Maybe I haven't been paying that much attention. I travel wearing a mix of dress/ converse/ boots type shoes but no issues so far. Neither has my GF had any issues (that I know of).

Naturally it is all anecdote data, I am not asserting that it is always like that.

Not my experience, at least flying from PT to ES, CH, DE.

Try wearing boots or shoes with thick soles.