Believe it or not, it wasn't. The 2.1Mbps was a burst. Normally, I would getting somewhere between .8 and 1.4Mbps(the latter late at night/early mornings). I June 2011 onward, speeds dropped dramatically to about .4-.6Mbps avg's during the day. By September, the average highs were in the low 400's(kbps). When I left Sprint in March, the last speed test I took only got up to .26Mbps.
3G speeds were already horrible when the iPhone arrived, and surprisingly, didn't really make speeds much worse.