Anyone who believes that Ueshiba sensei's level of physical skill will never be surpassed must, in my mind, have the following qualifications:
a) direct, personal experience with Ueshiba sensei's technique,
b) direct, personal experience with the technique of everyone else in the world walking the path, and
c) the psychic ability to see into the future
If you really believe that no one will ever equal or better Ueshiba sensei technically, then simple logic dictates that the technical level of Aikido will necessarily decline over the years until, eventually, nothing of much worth is left.
Why is Aikido so special? Why is it, and it alone, exempt from the same improvement that every other endeavour in human history has experienced? Why, in my experience, do students of other arts not play this pointless game of deifying teachers and setting up artificial, false limitations for themselves, their teachers, and everyone else? (Note: these limitations don't apply to me.)
I, for one, agree that Ueshiba sensei's technical skill level has *likely* already been surpassed by many people... some of whom may have even been his contemporaries. As far as saying that no one will surpass his spiritual level... what does that even mean? How is one person "more spiritual" than another?
If only Ueshiba sensei did "real" Aikido, then go ahead and call what I do "chocolate pudding" if you like... a name is just a name.
Besides... everyone knows that Bruce Lee could kick anybody's ass.