BK9 would make a great fighting knife but the BK5 is a lot lighter and quicker in hand. I also like the ability to choke up on the choil. Opens up the possibility of many more handholds. The 7s design was originally intended as a replacement for the Kabar 1211. Worth taking a look at too.
Other than the lack of a handguard I'd say the intention was a success, being only 2.2 ounces heavier while still having similar overall dimensions where it counts, and all the while still being a much stronger design for greater utility work.