I apologize as this topic must have been discussed at nauseam.
One of my colleague asked for advice. He will split his time between UK and HK and travels a lot, mostly discounted Y. He is currently BAEC but wonders whether MPC would not be easier to reach Emerald (DM MPC vs Gold BAEC). My argument was that BAEC is geared towards premium pax, while MPC is geaed towards frequent Y pax. So it will be much easier to become DM than BAEC Gold.
My calculation is that a return trip LHR-HKG will yield approx 12K club miles and 70 Tier Points. So he needs 10 return trips to reach DM emerald (after stepping up status for a year or two, but he should get status matched to Gold or Silver in the first year). On BA he needs 1500TP to reach emerald or approx 21 trips, which is unfeasible.
I am not trying to compare the relative benefits of the CX or BA emerald status as he will probably mix BA and CX in his flight pattern; just trying to help him asses whether he should move to MPC to enjoy higher status.

Anything wrong in my assessment?

This is correct assuming he files CX. If he files on BA then only YBH classes earn full miles on Marco Polo.

I thought when you reached each intermediate stage CX set the mileage back to zero ? in that case he needs far more than 120k to make Diamond in one year.

That's correct but OP seems to be aware of that.

I'd say it really depends on what your friend hopes/needs to get out of a program. Even though both are OWE, they offer very different benefits, no?

I know more about MPO than BAEC, but as I understand it:

-- Seat guarantee is more generous for Y flyers in MPO than in BAEC. On CX, the OWS/OWE-equivalent tiers can guarantee into lower coach booking classes, while in BAEC it's only full-fare Y.

-- If he misses DM one year and ends up as a GO, he can still pre-reserve exit seats on CX, which I don't think is possible for BAEC's OWS equivalent level.

-- RDM tier bonuses don't exist in MPO but do in BAEC. Although with BAEC redemptions require huge surcharges (CX surcharges are merely big )

I think it matters a lot which carrier he's likely to fly the most (CX also offers more frequencies at different times on HKG-LHR-HKG). I personally would lean toward MPO because the tier benefits are quite helpful. But if redeemable miles factor into the equation at all and he's willing to fly mostly on the BA flights, BAEC could still be attractive even at the OWS-equivalent level.

To clarify: I know OP didn't start out asking for a relative comparison of the two programs. But it is useful to think about that if only because, if something like RDM tier bonuses is at all important, the friend could end up being better off as a OWS-equivalent in BAEC than as a DM in CX.

Agree with the part of RDM. Not sure whether it is useful to you, but a 100% tier bonus is rather a large sum!
AFAIK, BAEC redemptions require huge surcharges only if you redeem BA-operated flights, but not on CX or other OW flights. I think I need someone to clarify on this probably.
And adding top on it, generally BA has a lower miles required for redemption than CX.
For example, BA needs 9,000 Avios while CX needs 15,000 Avios for a R/T HKG/TPE Y-class.

If you travel on CX mainly, there is no doubt that you should apply for MPO rather than BAEC.

It will take forever to get to DM. I think best to keep BAEC as he is emerald already, it will take 210k to get to DM

Yes, I think there is something wrong: economy long-haul should get him 70 tier points each way, thus he requires "only" 12 return trips via BAEC to hit Emerald.

If he's already Emerald via BAEC, depending on his recent CX travel patterns he may well be comped to Gold/Sapphire on CX immediately, if not even Diamond/Emerald.

But did he mention that his friend is going to travel on mostly discounted Y?? If that is the case, then shouldnt it be 35 tier points for each sector, making it 70 a round trip?

Def no comp if hkg based also given it is discounted Y class travel I highly doubt CX will even entertain anything - prob not even comp green

Not true - CX will comp Silver pretty freely.

I was comped to CX Sapphire from BA Emerald - as far as I can infer from the exchange of e-mails, they look at how much you've racked up on CX metal over the past year and then decide on that basis.

Based on discounted Y class?

Based on just discount Y class?

No.

But as others said, 100% Avios bonus, as well as a better expiration policy makes BAEC look better than MPC.

Also - since your friend is not HKG-based, a lot of potential benefits are potentially wasted.