Speed isn’t necessary for playing well, but speed makes it much easier to kill xenos.
Knowing when to go for the kill is almost all gamesense (knowing when the xeno player fucked up or is vulnerable, calculating that the reward (potentially eliminating an enemy player) is worth the risk (being capped/perma’d)).
Most things simply factor INTO gamesense-
E.g. competent fragger teammates massively decrease the risk and boost the reward by a lot, recognising the signs of overextension by xenos, mechanical knowledge, etc.
Now, having good gamesense is great, but when it comes to actually executing your decisions, you’re still limited mechanically. Your gamesense might tell you that you WILL kill a xeno if you chase, but how are you going to chase if you’re slower than the xeno?
How will you crit them if you’re too slow to keep up?
Will you catch them resting in time?
Is the risk-reward worth it when your chances of chasing and killing are lower, while your odds of failing to run away from an unfavourable situation rise?
Having high speed makes you much deadlier in offensive situations where your enemy isn’t really in much shape to fight 1v1. Heavy does not. It increases your TTK so you have more time to eliminate your target, but imo raising your TTK is irrelevant 50% of the time when the enemy team can just tackle and cap you, and also has multiple stun abilities in their arsenal. Being tanky helps, but not as much as speed does. I value heavy more due to the fact that it reduces attrition by a lot, e.g. less fractures, IB, etc.
Armour gives value when you take damage. However, it gives a lot of value when you do.
Speed gives value because it lets you prevent situations where you take damage, while also opening new situations to remove enemy players.
Point being, light armour is far from essential and a good player will frag no matter what armour they choose: but overall, light armour helps more than medium or heavy re: eliminating enemy players. Pick whatever suits your playstyle, but honestly imo any armour is ‘good’ except for medium, which was designed to be mediocre. (seriously, don’t take the M3, just take B12 at that point)