Saruman for or against Sauron?

[Kuruharan]

The Rings give some degree of 'power' to any possessor - according to their 'measure'. The statement in the letter is simply incorrect, as it contradicts statements made by characters in the story itself.

Not really.

Did not Gandalf tell you that the rings give power according to the measure of each possessor?

Do you honestly think the Ring, which is fundamentally a part of Sauron, is going to aid and abet another's quest to master it?

I find that unlikely in the extreme. The Ring would probably deceive that individual into thinking it was mastered and then betray said person to Sauron at the first available opportunity. The individual in question would quite likely be so power mad by that point that they wouldn't know if the Ring were truly mastered.

It is probably the seeds of self-doubt that reside in Gandalf (among other things) that make him uniquely capable of mastering the Ring. He would probably be less susceptible to its lies. Saruman does not impress on this score, and quite frankly, neither does Galadriel. Elrond might be a slightly different matter.

Sorry, but the easiest way out of this 'dilemma' is to dismiss Tolkien's statement & let the story stand.

There is no dilemma here. There are only some rather ill-founded opinions that some seem unwilling to let go of, to the point that if they can’t twist Tolkien’s words to suit them they will then just dismiss him out of hand if it is convenient.

Aragorn has the strength of Will to claim & use the Ring

Uhh…no. That passage doesn’t prove this at all. That passage proved that Aragorn had the strength and will to use the palantir (which was rightfully his anyway). The Ring and the palantir were two very different things.

Aragorn is lying to his friends

You are putting words in Aragorn’s mouth. He wasn’t claiming he could master the Ring.