Ignoring the other valid argument regarding 1v1s and keeping to just the practical theory and practice on counters... you clearly didn�t bother to take into account snipers and scouts have night vision and, while kills can be hard to secure sometimes ( depends on circumstances like ammo and health etcetra) , it is extraordinarily easily to get them xenos to fuck off with a good bit of health missing before they even close half the distance.
So yeah, I�ll repeat that statement for those two.
As for RPG, it�s slightly different but again, not hard to set yourself up places that aren�t easily sketch. If you�re continuously rushing forward as a RPG with the intention to remaining in the very front of all the marines you are gonna get targeted and fucked, it�s bad play on your part. Similarity that goes for B18. You wait, find an opportunity to push and fire. OR just set yourself up and wait for that opportunity.
As for pyro Spec, if you have an issue with light and still aren�t fixing it, you deserve to die. It�s not hard to use any of their flame fuel. Be it X B or that shitty normal stuff. Same goes for issues of range. If you have spitter issues, lay down basically any flame type and their ability to spit you down let alone them or anyone else instantly kills you ceases.... except of course like I mentioned the queen or ravager.
For those particular xeno classes to engage a specialist marine having a level of intelligence beyond UNGA DUNGA BiG GUN, they will be forced back or die. That goes for virtually all of them, even the ones with more close up equipment. Why? Because. Playstyle that�s decent lowers or straight up removes the chance to get fucked over by those particular xenos.
This same argument works with the vaunted, albeit shitty HPR. It�s actually not a shit gun. Many just use it as the wrong role. It�s not a gun meant to be lugged in combat as some sort of unga shotgun designed to insta kill. That�s not the purpose. HPR = Heavy Pulse Rifle = Machinegun = Covering and Suppressive fire.
Like spec, people don�t always use it to its purpose with positioning and tactics set accordingly. Then they die.
Issues in this case of warriors and spitty boys arise when people do dumb shit, like trying to be a vanguard player as a RPG or B18. Yeah you can do it. Yeah you�ll probably get kills so it looks like a good idea. Downside is staying on the front of the pack lowers life expectancy. Watch. Wait. Engage. Return to middle/ back of the frontline group. Repeat. (Goes for pyro, b19, Sadar).