There are ~6,900,000,000 people on Earth. Are humans still relevant?
Sheer numbers do not equate to relevance, only to a perceived or real difficulty in filtering by relevance in a given context.
For blogs, that means that while it has become very easy to find blogs about making ice cream, it is much harder to find the best blogs about ice cream making, especially those targeted at making really good chocolate ice cream – because most search tools we have today will start mixing in popular blogs about chocolate ice cream generally, or even those dedicated to making chocolate candy… Not to mention all the blogs that refer repeatedly to chocolate ice cream manufacture as a means to sell me more Viagra. Got enough for now, thanks!
Perhaps the way in which blogs have best maintained relevance is at the individual blogger level – it still makes a lot of sense to use a blogging tool to write regularly, to document one's experiences and thoughts in the moment, if only for later personal referral. In that sense, blogging is simply an umbrella term for all such diaristic activities, includingposts, and entries, and even updates.
Further, when such a personally-relevant blog takes off, and is maintained regularly, one can build immense writing skill, gain authority in one or more topic areas, and in some cases – as seen here and via the personal blogs of users like, , and – it can even lead to professional gigs, either writing, appearing in the media, or within one's industry. Oh, for that day to come for this poor rambler… But I digress…
Long story short – like everything else in life, blogs are what you make of them, and relevance is earned largely based on the effort exerted.