The article tries to blame Diakatana for the "twitch FPS" demise. (Until the latest resurgence of the last couple of Doom games).
I'd say, story based FPSs are what really killed it. Unreal, Half-Life, Deus Ex, System Shock 2, Thief, are amongst the early FPS's that went beyond run'n'gun, and took things to the next level.
Serious Sam came out in early 2000 trying to resuscitate the "run'n'gun FPS", and for some it did so nicely... for me... I was bored to tears after a few levels.
So, IMO... it wasn't Diakatana's failure that flattened that genre... it was the more involved / more interesting FPS's that didn't rely on "waves of enemies" to keep your attention. Basically the FPS evolved into more story based... whether it kept some run'n'gun aspects like Half-Life... or was more RPG-like that let you built stats like Deus Ex.
Get your games from GOG DAMMIT!