The value of Marriott BONV°Y Platinum Elite status is very subjective. It depends on, among other considerations, what benefits are important to you, how often and where you travel (difficulty of earning Platinum without the card and variable benefits received), personal financial considerations, etc.

There are numerous threads in this forum that discuss these factors; here is one.

Platinum and Above Elite Status Tips/Tricks/Benefits (Discussion Thread)

You may also want to check the AmEx forum for further Brilliant AmEx card discussion.

Getting the Marriott BONV°Y Business AmEx card would earn you an additional 15 Elite Qualifying Nights (EQN) annually, bringing your total to 30 EQN with your Chase Boundless Visa card. That is a good head start toward the normal annual Platinum 50 EQN requirement. If there is another double-EQN promotion this spring, that would make it even easier to reach Platinum this year without sacrificing the Brilliant SUB.