I'd concur with just ever so slightly better rates.
My conspiracy theory is that it's all just an operational streamlining to segment everyone with 8m in relationship balance because that coincidentally qualifies customers as "professional" investors allowing a wider of breadth of structured product to be sold because of that designation.
I've found the Citi private relationship manager to be more proactive with promotional rates to take advantage of such as 5% time deposits, hibor + 0 secured loans, etc. which seemed pretty good relative to other offerings. They do try to sell you high load and fee products, but I since I've quite vocally expressed my views on them, the badgering has quieted.
HSBC's premier and Jade RM for me were pretty unhelpful and I don't see much value from a financial stand point. I did use the Jade concierge though for valentine's day reservations to a place that I myself was unable to get. They do have some held tables via the service. That type of use isn't typical for me though so all in all I'd say not much value. If you live that high life though, then maybe?
I feel like you either cross the threshold or don't. But there really isn't much of a reason to pool your balances in one institution to capitalise on any benefits at priority banking services. There are some things you can do akin to credit card churning, like taking advantage of occasional promotional "new money" deposit rates etc by moving the money from bank to bank to appear as new money past a certain cutoff window. But it's effort for minimal benefit and you should probably use that time elsewhere. If you enjoy that kind of stuff like mileage status chasing, or credit card point maximization, it can be a similar game. But again, only if you enjoy gaming it; the financial value is minimal at best.
As far as card benefits, I'm only aware of citi and hsbc having specific debit cards for the HKD 8m tier. Both cards allow you to withdraw from a specific currency account while you're overseas so you don't necessarily have to pay an unknown FX spread if you already have the local currency in an account. That's a limited basket of currencies though. Given an alternative of using another card with good bonuses for overseas spending in miles / cashback, the benefit of not conducting FX each time is minimal. It's probably just useful going to an ATM.