I did some work with Charles Forgy, and if I remember correctly, the challenge with RETE was that it scaled very well with a large number of rules (as you note)

I did some work with Charles Forgy, and if I remember correctly, the challenge with RETE was that it scaled very well with a large number of rules (as you note), but it scaled very poorly with the size of the data set against which those rules were applied. He subsequently developed versions of RETE that addressed some of the weaknesses in the original algorithm, but the subsequent versions were not released in the public domain. For example, RETE3 (early 2000s) is now owned by Fair, Isaac.