I agree. Generational guys usually excel at an early age compared to #25 picks, though. That's not to say Auston has peaked or anywhere near it, but you might see more of an improvement in defensive awareness than in goal scoring, for instance.
Also, Pastrnak had injury problems and played on 3rd and 2nd lines under a Claude Julien scheme his first two seasons, so it's not fair to compare those first year and second year (or even second year and third year to compensate for age) to Matthews's two years in the league. Hell, you'll never get a fair one for one comparison.
Since Cassidy took over, Pasta has scored 47-59-106 in 109 regular season games, plus 6-7-13 in 8 playoff games. Comparing is useless, but Boston's situation at centre and their first line's combined salary are both pretty damn good for them.
Pasta was great right away too. He wasn't getting the TOI and PPTOI (28 seconds of PP time per game in 2015-16 compared to 3:05 this year) and had a worse average quality of line mates than Matthews (obviously much better now, though). He was kind of at the stage DeBrusk or Heinen are right now. Hope they can break out like that too, though they're slightly younger or slightly older than Pasta respectively and won't exactly fit on the first line anytime soon.