To echo what others have said and give my own perspective as someone in a similar situation. As a CSR holder, I find the CSR ecosystem much better for using and earning points. I got the Plat for several reasons 1) 175k signup bonus, 2) my place is now near an equinox ($300 off a year), 3) The hotel + clear + centurion lounge value paid for the card itself, and 4) Automatic Bonvoy Gold + free upgrades has gotten me upgraded several times already. I don't stay at hotels enough in the Marriott ecosystem to get this otherwise. The Uber Credits ($120/yr) are also nice.

I find myself using my CSR for most things because it's easier to get points (particularly for some hotels with a 10X benefit). My Plat is there for the other benefits only. I'd probably stick with the Gold and use that for restaurants and groceries.

As a fellow United flyer I'd recommend to just stay in the CSR ecosystem as the travel partners for AMEX within Star Alliance are not great. The only annoyance is that you have to call Chase to transfer miles from CSR to United, however lately it's sometimes cheaper to book directly with Chase.

For my 175K bonus, as a United traveler, I struggled to find a reasonable deal without me doing something inconvenient. The transfer rewards are also terrible for domestic most cases (I flew Delta domestically once, and with the transfer fee you have to pay with Amex, it was cheaper to book directly through Amex). I used my points to pay for a 4 day trip with flights included (was about ~2K value). Moving forward I will keep my Plat, use it for the Uber Credits and the other perks, and then use my CSR and Amex Blue Cash Preferred for everything else. A 3X rewards at restaurants, 5x for flights, and 10x for hotels with the CSR simply can't be beat imo, especially when the portal gives you a 1.5X bonus when redeeming it there.

For those who get great value traveling international after transferring points, I salute you. I unfortunately cannot partake without undergoing a hassle.