Also, keep in mind that Fotis is a well known promoter of his way of doing things. If the facts don't always completely line up, well no biggie
Basically what 99,9% of users will ever need
Did he take a poll? I guess only .1% of all users like to use 8,000+ Joomla extensions on their site, change the user profile or registration forms, create a filterable search of content, have more then a few cck fields, fully customizable admin and forms and a unified back end user interface, etc.
I don't know about performance, but I think the difference is negligible if the site isn't huge (less than 1000s of articles/categories). Even if it is big, I can't confirm anything but I've heard the Seblod guys say that the Search Type can perform very well on large sites. Also with any website, having the right server and server configuration is always going to be an important factor, probably much more so than K2 vs. Seblod.