It often comes down to player skill, timing of engagement and spec.
Combat rogues can beat warriors and/or if they do the right skills/plays right.
It is very hard to generalize classes in Wow like this esp in vanilla as it again often comes down to the player, spec and strategy.
If I may generalize:
Frostmage+Priest(shadow) can often beat warrs because they have shields which absorbs damage leaving the warr without rage = less action more death. Ofc the warr can get the engage and get a critt, massive rage and bam the cloth died instantly but that is more likely in world pvp.
Hunters eat all classes except warriors because they hit hard and can't miss imp overpower (arms) - they outdps the hunter because their slow is also stronger unless the hunter is better and manages to kite forever. (warrior is bad in this case).
Shamans eat most classes that don't kill them with insanely lucky crits (can't outheal or escape shaman in most cases) or some uber kiter such as a hunter keeping max range.
Otherwise, purging magics, shields, hitting like a truck (enh) It's hard to lose as a sham.
Possible counters is rogue and mage because of sheep+burst+cspell(or Pom pyro spec) if the sham is unlucky he doesn't grounding in time that would absorb it. Rogue because of cc, heavy dps and evasion - the rogue may outdps the shaman, using most cooldowns but I would often bet on the shaman if he can play.
There I just gave some generalizations and possible scenarios but we could argue back and forth for days.
That is why I love vanilla Pvp, it's unbalanced in a balanced way. It is usually strategy and skill behind it.
Oh and Rogue's are 'God'.
No but there are a thousand strategies as a Rogue. It comes down to strat and skill of player.
Can cause great CC, best class 1v1, huge slow, anti-healing, interrupt cast and can deal massive burst damage and/or perpetual dot.
