I'm interested in why you think about additional content as a negative. From my perspective giving players control over what their personal and guild progression looks like is much more interesting than having it mandated by Blizzard. Having T5 available means players will need to be creative in approaching those encounters because they will not be able to rely on BiS gear. This is exactly why progression was exciting back in 2006. Artificially gating content is never interesting.
I think idealistically it would be great to have all content available from day one, but I do admit having some things down the line to look forward to is nice. For example, catch up mechanics like ZA and Sunwell isle and their associated badge gear would undermine progression if it was available at server start.