Hey Mike, thanks for your interest.
Hinterlands has been running a good while now, and has enabled me to try out lots of variations on the original rules. Yep, back in 2013 I trialed increasing attacks rather than improving THAC2. That was a while ago now, but from memory I think it worked out "okay". I spent quite a while figuring how to "balance" the number of attacks and their adjustments in order to produce a smooth attack power progression. That was all nice on paper, but I think in practice it was a bit fiddly.
The original D&D normal combat rules may seem coarser (they are), but ultimately they are simpler to run. At the game table simplicity always trumps sophistication because simplicity facilitates a good game pace.
So if I were to do it all over again now, I would ditch my finicky table of adjustments, and simply go for the original game's "Fighting Capability" stat, where each "Man" worth of FC equates to an attack (using the first row on the attack matrix). If you don't have the original game, you can look forward to FC appearing in the forthcoming DD V5, or simply substitute number of HD for FC (3 HD = FC of 3 Men).
Hope that helps
the Elf Medium (MV 12", AC 9, HD 1, hp 1/1, AL N) great cloak, lantern
; spells: color spray; scrolls: sleep, sleep, charm person
Hirelings: Georges; torch