In this game everyone is the same as you are in terms of hps, armor, movement etc. This is why you can take a fairly accurate guess at how fast the enemy can move and the shots he can take. There's no headshot multiplying the damage you inflict meaning it stays the same no matter where you hit. Since headshot isn't a mechanic and instant killing becomes hard as result, killing on sight isn't always the best choice and gameplay goals change. Some players who reach high skill to obtain perfect aim learn to stack armor etc in order to control the map instead. They learn what paths to take based on where things spawn and how to choose between mega and armor when these spawn at the same time. The armor system is pretty much the only one in the arena realm that always gives you something to do after you take an armor or something and chase after another pick up, while too many arena fps fully stack the player and send him chasing after the enemy in the middle of some map rather than having players come up with plans.

tldr, there's a million valid reasons why arena fps die but people keep coming back to old simple quake stuff to get more consistent mind reading than in most fps. It's great