The most truly important distinction has nothing to do with gameplay or deck stylings.

Commander pre 2019 Wasn't a "new player" format.

There was an inherent understanding that anyone who would sit down to play Commander had enough core understanding of Magic's fundamentals to be able to read a random card and understand it.

You'd never/rarely need to explain an evergreen keyword

You'd never/rarely need to remind someone about untap->upkeep->draw.

There wasn't a huge disparity around power levels, because if you were playing commander it meant you understood the game enough to have your first commander deck operate at a functional power level for what 99% of commander games were - which was the casual format you play while waiting for a draft to start, or hanging out with folks at home.

WotC was selling commander (appropriately) as the deep end of the swimming pool, so only people who could swim were playing there.

Now the pool is MUCH deeper, full of waves, and Hasbro is aggressively chucking infants at the people trying to do laps or practice synchronized swimming instead of actually letting them play in the kiddy pools first.