I just fired up the WoW vanilla emu server and rerolled a warrior, and also recently bought MoP (been bored recently, OK). In vanilla, I probably died 3x on the first dungeon crawl in Elwynn forest, I died to murlocs in the lake, I had to group for the named mobs or I'd die, needed to watch for pats and multi-pulls etc. All through Pandaland, I don't think I was ever in danger of being close to death once. Didn't talk to anyone in the world either. It's quite a change. The combat systems now are more complex, I guess, but the world design of vanilla was much less forgiving - and I really think it added something to the game.
Cool story bro.
Lets have a look at a few things that pretty much invalidate the bullshit you're spewing. You've stated that it's the world design in vanilla that made it tougher, then talked about combat mechanics (which haven't changed at all since vanilla).
Firstly, the vanilla warrior is a vastly different beast than the warrior of today. Two abilities that come to mind, Victory Rush and the reworked Second Wind. These two abilities (in their current incarnations, and Victory Rush altogether) never existed in vanilla. The reason you never felt threatened in MoP is because you have these abilities. Second Wind makes a warrior pretty much unkillable, which is why it's getting toned down a little bit in 5.2.
Jade Forest in MoP was pretty cruisy, by the time I hit Townlong Steppes, shit started to hit hard, real hard -- and pulling more than 2 meant cooldowns had to be used to prevent a death (depending on class and spec), my Blood DK just gives no fucks and pulls everything, my Arms warrior the same, my rogue had to be selective, and my warlock had to have the right pet out for the task.
The final reason (and in my honest opinion, the real reason) you never felt threatened was because you're actively trying to take a shit on MoP (and assuming you made it to 90) you'd remember that there were Virmen types that stacked a bleed so fast, and hard, you'd die in seconds if you pulled 3. The area those Virmen are in is PACKED with them as well, so pulling more than one was always on the cards. Respawn times are fast enough that you can't afk through the area, and slow enough that you don't get zerged right from the start. It's either your memory is selective to give weight to your opinion, or you're just flat out lying.
There's rare mobs in MoP that are capable of 1-2 shotting even raid gear 90s, you can kill these 90 rares under leveled and under geared if you know how to deal with their abilities and your class (that silly monk bitch in Townlong Steppes with Spinning Crane Kick, Chi Burst and Healing Mist. There was nothing in vanilla with the complexity of some of the rare spawns in MoP, and while they are not really that complex, they sure beat the shit out of Hogger.
A level 9 warrior in vanilla doesn't have any fucking cooldowns to pop, they don't even have defensive stance. Put down the crack pipe and step away, or, you know, actually look at things subjectively instead of trying to ride the nostalgia train to nowherefastland.
Also PvP server... There's tons of players in the upper level game doing dailies and what not, making places like Townlong, the Wilds and Dread Wastes a fucking death trap (and a shitload of fun).