I own three Iwatas, two mid range and one from the top, I am in no position at all to state that they are the best brushes ever, but do what I want them to do and done give me headaches, I don't ever modify anything, if I thought it needed modifying then I would clearly have the wrong tool and would been better buying something else, since I get what I want out of them I have no intention to buy anything else.
To get the answers you seek you need to go to Don Wheeler's website where he puts brushes through their paces and gives a good honest review on how they behave and perform with no bias whatsoever, your not going to find that here no matter how you word it.
We've had a few members over the years who's goals seemed to be to shoot down everything anyone else said, asking what appeared to be genuine questions only to argue the toss about the answers they got, folks who never posted a single piece of work but we're full of opinions, they generally don't last long.
I've read every single post in this thread and even though you've explained what your looking for I can't see any point to at all too the thread, we've had the same dusussions over and over to no useful end.
If you are happy with what you have now and it does what you, you don't need to ask about other brushes, I'm happy with what I've got even if I have the worst stuff ever.