PS4 is a monster and PS5 has a chance to dethrone both PS4 and PS2!
No console will sell more than PS2. The PS2 sold so well due to the large number of third party exclusive games it had. If you wanted to play a game, even a third party game, you had no other option but PS2. Now third party exclusivity is very rare, when it happens it is timed exclusivity (usually 1 year). Also it was the cheapest dvd player on the market. But now streaming is becoming more popular than buying movies in Blu-ray.