1) Many of his beats are loops, but I will give him a pass because that's hip hop...
2) The rappers who rap on his beats actually "help the beat more than the beat helps them." The "We Gon' Make It" beat was given to Ras Kass and nothing came of it, until Jadakiss blessed the track...
3) The beat battle vs Just Blaze showed me The Alchemist doesn't really have that many certified all across the board hip hop bangers...In other words, bangers that fans of different forms of hip hop can actually say "yeah, this knocks.'
He doesn't have these kinds of beats, even though he's been around for years and he has an extensive discography...
Basically, the Alchemist is a "Cult Classic" beat maker...You have to be in that "Real/Pure Hip Hop" lane to hear his music...
To conclude,
The Alchemist is NOT UNDERRATED in the grand scheme of hip hop, because he just hasn't consistently made blockbuster beats...
He is not in the same league as Kanye West, The Neptunes, Timbaland, Irv Gotti, Dr Dre, Trackmasters, and other "Major League" beat makers who can make a rapper go platinum off of one beat...
He is overrated because, he has a cult of followers who believe his beats are that hot, when the majority of fans and rappers in the "major leagues" don't seem to think so, because they don't run to Alchemist for that "fire" that will take them over the top...
I am an amateur beatmaker who samples and tries to do my own composition, and there are only a few Alchemist beats that have made me just want to give up beatmaking...And that's how I judge how good a beatmaker is...
If I hear your beat and feel like "damn, this is too hot...I might as well just stop making beats, because I don't have the creativity to make such a beat" then you are a top beatmaker for me...
With the Alchemist, I know if I hear the original sample, I will know exactly how he made that beat...
That's why I am kind of

with "Crate Diggers," because they use rare samples to trick us into believing that they actually did something "creative," but when you hear the original song, it's just straight loops...
And because of this realization, I have come to the conclusion that beatmakers like Lex Luger, Young Chop and others who don't use/seldom use samples, and make songs that bang across all forms of hip hop, are actually more talented and creative than the majority of sample based producers...
It's just my opinion...