Whom are you arguing with? I just did a word search on this thread to find the word "best". It seems like the only one to specifically make reference to yoga/pilates being the best for flexibility and/or specifically for aikido is YOU. Got back and re-read and you'll see that no one else said that!
Also, you seem to have a hang up where you think "lengthen" means "grow" and the rest of the folks on the thread all seem to agree that "lengthen" is a perfectly normal way to describe muscle activity going to a "relaxed state". I suggest you let it go and return to a "relaxed state". You might find that you'll "grow".
No one needs to be able to do a full Chinese split for aikido. But I think we agree that some flexibility is integral to aikido. Especially mental flexibility...