Stunning and countering a stun

Hey guys. I've been wondering about this game online, as I just bought it recently. I've played for a few hours and I can't tell if countering when someone tries to stun you is glitchy, luck based or just flat-out broken at times. I understand that killing someone takes priority, but it seems like there are times when I can CLEARLY see a human player, who is a target, b-lining straight for me (and not using the charge ability), and I face them, lock onto them, and start mashing the X button... and they still just casually stroll up in their animation and box my ears, knocking me to the ground. Other times I'll be doing a sneaky approach to a player who is hunting me and he'll be focused on a teammate, I'll sneak up behind and start to stun him, then he counters me immediately and stabs me up. What is even more frustrating is that people also seem to go through my smoke at times and kill me, yet I'm always being stunned by smoke. Is this some type of latency issue or something? Basically, I'm asking the veteran players out there... what's the deal? Is mashing the X button for kills or B button for stun a bad idea, as in you need to be super precise when you hit the button, or is it just straight up luck based off of your network connection?