Last time I checked (which admittedly was over a year ago) people were saying that Creality sourced their PEI sheets from a reputable company (which name has also slipped from my mind) so they should be good quality. On the other hand, I believe Creality used to put genuine Meanwell PSUs in their printers a long time ago, and they changed to cheap unbranded ones to save money later.

Some thoughts though.. The print surface is thin and flexible, so if it dips like that I think it's more likely the carriage under the bed that is bent. I.e. replacing the print surface might not fix it. A glass bed might be able to even it out, assuming you don't clamp it down too hard, since glass is also a little bit flexible. If you want smooth glass, it's usually cheaper to get a mirror cut to size than buying a printer bed. The reason for using a mirror instead of regular glass is that mirrors have to be very flat in order to not distort the image, while window panes can be a little uneven without anyone noticing.

Personally I'm not a huge fan of glass, but here are some pros and cons so you can decide for yourself:

Pros - Can compensate for a bent bed carriage. Cheap (especially if you get a mirror). Quite durable, lasts a long time. Withstands chemicals, for example if you need to remove ABS residue using acetone. Cons - Heavy, which will limit the maximum acceleration you can use before getting print artifacts. Not the best adheision so you might need to use glue or something to improve it. Unlike PEI/steel beds you can't bend the sheet to pop the model off, so you have to wait for it to fully cool down before you can remove the print (can take around 30 minutes)

But with all that said, you have a probe so it ought to be able to compensate for that dip in the bed easily. Maybe increase the number of measure points if it's causing problems?