I love sweeping, blanket statements like this, probably from someone who has never owned Media Composer and probably owns a cracked copy of the others. How is AVID slow? I've had less problems scrubbing audio frame by frame and keeping up with AVID then FCP.
Each NLE has advantages and disadvantages, I own Adobe and Avid both for this reason. One good thing about the new Final Cut X is the rendering on the fly, that does speed things up and points to the future.
AVID's strength was always stability and media management for large projects. Not having crashes and media offline notices keeps speed up. But one of the best features about recent Media Composer versions has been the ability to mix source frame rates and types in one timeline, WITHOUT any transcoding or re rendering time lost. Just drop in and use. WIth documentary being made of endless clips from endless sources, this is a real timesaver.
And then phrasefind, this is a nifty piece of software that associates script text and the source clip instantly. Again, a real timesaver for scripted work or documentary interviews that are transcribed. Just search for the words you want, and bam up comes the clip.
As for clunky, fast editors work off of keyboard shortcuts, an editor can be equally fast on all the NLEs as far as I'm concerned.
Half the time when someone thinks an editing system is slow or clunky, its the media access speeds that are the issue. Raid through a pci or thunderbolt vs one external USB 2 or firewire drive and bam, problem solved.