As a huge face fan, I understand what OP is getting at, but it is just his opinion. On a side note, I just booked tickets to see him next week for the first time in concert.
The Fix is and will always be Face's most mainstream album. For anyone who hasn't listened to Face, you start with The Fix because it is the easiest to listen to. Most Face fans will have other albums as there favorite. Face is my favorite, and the Fix is somewhere near the top. Lyrically it probably isn't even in his top 5, but the production is probably his best.
As for the content, like OP mentioned, the reason why it isn't the usual dark lyrics is because Face was in a much better place. In his book, he talks about this album being the first time he got to make music with freedom and on his own terms. He was in a happy place when he made The Fix.
The album that is the most lyrically underrated is Made. I even read an article or interview where he even said the same. The Diary and The Fix are probably his two best albums, but you can definitely make cases for The Untouchable and his really early work.
I think the reason why it got so much attention was that this album gave him mainstream success. Not everyone knew or listened to Scarface before The Fix, not the case after he released it. Scarface's music isn't for everyone. Most people who don't enjoy Face will say The Fix is the only album of his they can listen to, mainly because it is mainstream and has great production.