If we don't count Cups and Conn Smythe (mostly team awards), don't count Calder (because it's not among 'the best player' awards, even if AO won it over 102-point Crosby) and generously give Kucherov all the trophies he hasn't won
yet this year, then:
Kucherov has 2 Art Rosses, 2 Harts, 2 Lindsays, 2x1st and 2x2nd NHL AST.
Ovechkin has 1 Art Ross, 3 Harts, 3 Lindsays, 9 Rockets, 8x1st and 4x2nd NHL AST.
Malkin has 2 Art Rosses, 1 Hart, 1 Lindsay, 3x1st NHL AST (a stronger poistion though).
100-point seasons: 4-4.
Top 5 point finishes: 5-5.
Goal scoring obviously massively favors Ovechkin. Both guys are main scoring forwards not known for their defensive game. A massive style difference of a finesse playmaker vs aggressive goal scorer. Ovechkin has another dimension as an effective physical player.
I think it's clear that Ovechkin has achieved more, in an era when scoring was more difficult, on a much weaker team as well. But one more season with major awards, and it will be perfectly fine to reason that Kucherov's peak is as good or better as Ovechkin's was.
What makes it very difficult to argue Kucherov's overall legacy over Ovechkin is that AO is the best of all time at what he does (scoring goalz) and, God willing, will have the numbers to show it, even over guys who played in ridiculous era like the 80s.
And while it's relatively minor for their NHL ranking, it would be a bit bitter to call Kucherov 'the greatest Russian to play in the NHL' when he has zero championships with the national team. Not to diminish Kucherov for Tampa's long PO runs lol, or not to say he hasn't been great for the national team, but... still.
So for you, you have to explode at 20 and drop in level from 25 to be more considered than guys who explode at 24 and continue to progress until 30 ? It makes no sence.
It's true that hockey community is notoriously conservative and somehwat biased towards the players who were high flight prospects, high draft picks and early bloomers.
But arguing that it's not easier to score today than it was 10-15 years ago is just... strange. The league has made numerous steps to increase scoring: different policy towards enforcing the rules (no uncalled interference/obstruction all over the ice (that consequently led to near-extinction of defensive defensemen), 3v3 OT, goaltender equipment, less physicality (flying headshot charges were the norm during 'the big 3' prime). And it's good. Skilled players prevail now.
Also, it's not like 'the big 3' fell of the face of the Earth. If we consider 2017 (1st McDavid Art Ross) the start of the new era, season by season:
2017: Crosby 2nd in points and wins Rocket (44 goals), Malkin 3rd in PPG among regular players (Kucherov 4th), Ovechkin has a garbage season.
2018: Ovechkin wins Rocket (49 goals), Malkin 3rd in PPG among regular players (Kucherov 4th), Crosby has a solid season. Ovechkin has his highest points total since 2010. Malkin has his highest points total since 2012.
2019: Ovechkin wins Rocket (51 goals), Crosby t-5th in points, Malkin has a weakish season. Kucherov wins the Art Ross.
2020, shortened asterisk season: Ovechkin wins Rocket (48 goals), Malkin is 7th in PPG among regular players (also has his best PPG since 2012. Kucherov 10th), Crosby has a weakish season.
2021, crappy COVID season: first year all 3 aren't really that impressive: Crosby (34 y.o.) 10th in points, but Ovechkin (36) and Malkin (35) have weakish seasons. Kucherov resting on laurels))
2022: Ovechkin (37) 4th in goals (50 goals) and has his highest points total since 2010. Crosby and Malkin miss a lot of time and have solid part-seasons.
2023: another weak season for the old guard: Ovechkin 10th in goals (40 goals), Crosby and Malkin 16th and 26th in points. However, Crosby (35) has his 2nd best points totals since 2014.
2024: similar to the last season. Crosby (36) again has his 2nd best points totals since 2014.
So, answering the question 'why wouldn't old stars score more than when the scoring went up - they... did exactly that. All three had been world class before hitting ~35, when it's completely expected to decline.