Far from being an expert on the Japanese language...I took a beginners Japnese class some time back and the teacher was a native Japanese lady. She said that "Sensei" referred to a master of a given trade. Though generically it can be used as "teacher" it really refers to someone who is a master at their craft. Using that definition I find it hard to believe that so many can be a sensei.
I fear the word "master of an art or trade" has lost much of its original value. Just about everybody seems to claim mastership of an art or trade. There is no longer a standard to reach for, many people seem quite early in their progression of any art satisfied with the level they have. In a similar way the word sensei and the relationship sensei - montei has lost much of its original meaning. Especially in Aikido - with the exception of the more traditional dojo. In particular the old ryuha have maintained much of its original meaning and purpose. Personally I prefer the old ways.