Since the connector won't be handling battery current, but rather phase current, there isn't a way for us to tell you what battery current it can handle. Because phase current vs battery current varies depending on the motor speed vs it's load, and other factors like which specific controller is being used, and exactly what it's settings are, and which motor is being used, you can only really rate a motor phase connector for how much phase current it will handle, not battery current.
The Grin Tech page doesn't list it's maximum *continous* phase current capability, but it does say this for the peak:
This connector has much larger phase pins than the Z910 and is available in up to 4mm^2 thick phase wire (slightly larger than 12 gauge) which has shown to be reliable for up to 100A currents for short times.
I don't know what motors other than Grin Tech stuff that already come with it on there.
As for "better" connectors, it depends on your specific needs.
Do you need waterproof?
Simple disconnect, or more secure?
How many wires do you need in total? (three phase, plus how many signals? 5 hall wires...plus any thermal or speed sensors? Etc?)
What gauge wires do you need it to handle?
What currents do you need the contacts to handle?
Connector cost budget?
Connector size limitations? (does the connector have to pass thru anything? Do you have to be able to get the axle nut off of the cable? etc).
Keep in mind that generally the "better" connectors I can think of are not going to come already installed on anything, and would require you to crimp the pins on each wire yourself and insert them into the connector shell, which you probably don't want to do.