You wrote: But don't you think I should DO SOMETHING to help him see the deception of the WTS?
No! He sees it and is self denying he's seeing it. Keeping rapport is doing something. All Witnesses I know become angry when I tell them what they already know and are denying. The ritual meetings' main purpose is to reinforce the denial that's required in order for the person to continue. Initially they were called "consolation" meetings and the attenders were in morning because their expectations of the promised apocalypse were not met. They "re-set" each other at meetings.
They can also "re-set" by chanting, talking to one another (called up-building), and reading their books and tabloids. Whenever I have been so foolish as to challenge a believing Witness, they have always chanted, lashed out in anger, walked away, or all three.
The question is: what's so lacking in your son's life that he's getting his needs met by a religious high control group like Jehovah's Witnesses?
You wrote: By gently and lovingly asking strategic questions about the WTS, don't you think he will eventually realize he's been duped?
My dad was born in 1921, raised by Bible Student parents, became a zealous Witness adult, saw every single thing the Witnesses ever taught fail, saw the new teachings fail, saw the excuses fail and he saw it all as a test by a cruel and punishing god. He died as a rabid Witness, shunning me the last 12 years of his life. The failures he saw as a Witness made him a STRONGER Witness.
About the only consistent thing that I see in helping Witnesses to quit the group is a social setback. There is hope, because those do happen pretty frequently. That was my catalyst to quit the group. Of course the shunning and snubbing ensured I wouldn't return.
My dad had several serious social setbacks but he was able to separate the Witness people from the Jehovah's Witness ideology and carry on. Every single thing that would make a normal person quit the group, like seeing failed predictions like he saw, and being socially disrespected like he was socially disrespected, made my dad a better Witness.
I finally realized my wishes for my dad to see the group for what it is, and quit was selfish of me. I entertained a fantasy in my head that someday my dad and I would have a good relationship. But that's all it was. A fantasy! I decided to let it go and accept reality. The reality was my dad would stay a Witness and he would not become a better father but he would become worse. With that expectation, I had a concept that he could live up to and we both could find peace apart. When he died, I didn't cry.