Titebond 3 sucks is why lol. Jokes aside, titebond 2 is 1/3rd the cost and if you apply a proper finish, then water fastness is irrelevant. Titebond 3 is water RESISTANT, not water proof, and ultimately is just a needless expense. Can be extra insurance in specific use cases (i use it on kitchen and bathroom stuff for instance), but usually isnt necessary.
So sorry, but you are incorrect. From Titebond's website, this source: http://www.titebond.com/community/the-big-three
Titebond II: 'In fact, it passes the ANSI/HPVA Type II water-resistance specification.'
Titebond III: 'It passes the more stringent ANSI/HPVA Type I specification, classifying it as ďwaterproofĒ.'
It is true that Titebond III costs more than Titebond II, but Titebond III is the best wood glue I know. I can use it in any application, including those where Titebond I or Titebond II would be sufficient.
The cost of glue is not a factor in my projects. I buy small bottles, and they usually age out before the bottle is empty. Why keep multiple glues around? With that consideration, having Titebond III solves any wood glue issues I may encounter, even though it is overkill for some projects.
Caveat: Titebond III dries more gray compared with Titebond I and II. In theory, you should not see the glue line with a proper tight joint. In practice, you might see it and that may be a consideration.