* Calculating this should be inverted: counting how many 1st tier players were drafted top-3 rather than how many of said picks become 1st tier as that is - as any bin would be - a very low number (though, you could do a comparative analysis in this way comparing top-3 picks to lottery, non-lottery 1st, or later).
From the vantage point of how many elite players were drafted top-3 in the last 20 years, let's say that this is the list you're working with
-Lebron James
-Giannis
-Steph Curry
-Kevin Durant
-James Harden (doesn't really belong on the list right this second, but recently enough and for long enough that I would consider him belonging)
-Joel Embiid
-Nikola Jokic
-Kawhi Leonard
-Anthony Davis
-... Luka? (right?)
Well from that group, we have:
Top-3: 6
Lottery: 2
Non-lottery 1st: 1
2nd round and later: 1
You'll get a similar outcome if you swap a player from the list here or there with Jayson Tatum, Chris Paul, or Paul George (I think it falls off after this point).
If you're counting top-3 versus the field, that's probably greater than or equal to 50% of elite talent is drafted in the top 3.