Not true. Fansubs aren't getting slower. Bakasan recently stopped subbing naruto completely, and he was the fastest subber as far as I know, and Bakafish said something about being unable to sub naruto for a month. So that leaves Shin Otaku and Anbu/AonE to sub it, both of which who sub for quality and not speed. I'm not sure if there are currently any more naruto fansubbers.

Though Anbu/AonE do seem to be taking extra time lately.