Look, as much as I hate to defend him (since he neg repped me for daring to disagree with him) he's not completely wrong.
He's at a vastly different point as a player. He has capped multiple toons and is now (probably) in a guild that mostly does Amrath, Epics, and other endgame content.
You're looking at a static group with restrictions, and you're a newer player. You need and want different things in a build.
You're not going to be running into tons of creatures with SR before about level 15, but once you get there, being pure-classed will be a benefit.
The multiclass build I suggested, however, has better saves, better hit points, and in general has some training wheels and survivability features that will eventually get outpaced by the bad guys. But if you're going to be spending a lot of time going from 1 to 14, you will probably appreciate them.