That's not strictly true. Being an effective pvp player, knowing how to counter everything is important.I wouldn't say heavy weps was useless, rather you had to know how to use them, and if you knew that you would deal insane dmg in pvp.
The poise system in darksouls didn't work very well.
Just look at the video you posted (Post #9) he can just continue waving while taking multiple hits from small - mid sized weapon, you where pretty much a walking tower if you had enough poise.
Dark souls' poise system's biggest flaw is that people can just poise through attacks then backstab the opponent.
In that video, rosie is basically a skilled player killing some beginners. If she is using dark wood grain ring, and a katana, she can kill them much faster. Heavy armor means slower rolling speed, rosie has fat roll so she won't roll at all. Wielding heavy weapons in heavy armors take much more skill than any other play style. Play without lock on, without roll backstab, having to effectively parry are much more challenging than dark wood grain ring, hornet ring, chaos rapier +5 back stabbing. You can try it yourself, build a poise monster and try to R1 your way to victory. It's not easy.
In demon's souls, no one is wearing heavy armor because everything stun locks. Sure dragon bone smasher is a cheating weapon, but there are more cheesy tactics such as blue blood sword stun locking. Demon's souls pvp is pretty weak comparing to dark souls. Dragon bone smasher is probably the only heavy weapon that is any good, that is also because of the bugged cursed weapon enchant spell. Demon's souls pvp is much less refined and fun when compared to dark souls.
Also, you still hasn't given your evidences of why making the game less random is a bad idea. My poise suggestions can be Incorporated into the game without losing any thing. Players who is wearing full plate armor will have more inertia and will less likely to be knocked around. Weapon parrying is less effective than shield blocking and small shields are easier to be knocked off than large shields. It's not that alien of a concept.