I think his main concern is whether MBB will send love letter ask to prove those are personal transactions but not business transactions.
Heard a few cases recently, but not first hand info, can't comment much.

I'm charging 5 figures monthly for business purpose, same merchant...so far no issue

Ahhh okay. We're in similar boats then. I also use my M2P Amex for a majority of business charges, though mine are mostly in USD. Have plans on shifting to the platinum charge card later this year so I don't need to keep monitoring the credit limit and paying it off before statement date just to make space. Fingers crossed MBB doesn't take issue!

Directly no, but indirectly yes

Example you want to redeem ANA flights

You are unable to redeem directly with MR points

But you are able to redeem krishflyer first, then use krishflyer to redeem ANA (both being star alliance members)

Earning air miles and redeeming air miles are two different knowledge.
Both are equivalently important and too big to teach from basic.
Play with redemption is the key, the more you play, the more you master.

I will suggest you to start with the following article on KF - Star Alliance redemption.
https://mainlymiles.com/2020/06/19/which-st...risflyer-miles/

Similarly, you can use Asia miles for OneWorld redemption.
These two FFPs are most common for us, with plenty online guidance to help us too.
Master in these two before explore other FFP.

Unfortunately Amex doesn't offer us too much option.
The 3rd useful is probably Emirates and followed by Etihad.
Always understand why you redeem certain FFP.
Consolidate into few FFP rather than keeping plenty FFPs with little miles.
We try to avoid orphaned miles which we can't redeem via CC.

this year MBB did not waive my annual fee after 3 years of waiving
they offered me 500k points
do u guys think its a good deal?

Few weeks ago i request transfer treatpoints (M2P) to Kris Flyer, it took less than 10 mins to reflect in my KF account, wonder why MR..especially plat card take up to 21 days! sound ridiculous ><

My last transfer from MR to KF, CS told me up to 21 days too but it only took 5 days