Electronic – USB single chip ESD protector for two connectors through a power switch

The datasheet for the TPS2115A you're considering lists its ESD ratings as 500V and 2kV (depending on the model) in the same 'Absolute Maximum Ratings' table which you're seeing the 6V limit.

I read that as 6V being the maximum sustained operating voltage (although proper operation above 5.5V is not implied).

While your teammate is correct in in his position that a 5V TVS device will not prevent the input voltage from rising above 6V during an ESD event, I believe that he is incorrect in saying that any ESD will automatically damage the device.
According to the datasheet, you don't need to ensure that an ESD event doesn't raise the input voltage above 6V - you rather need to ensure that it doesn't exceed the 500V or 2kV limits.
How you do that (filtering, TVS's, whatever) is another question.

Choosing a different device (with a higher voltage rating) does not give you any automatic assurance of ESD protection.

You need an USB application-specific TVS array with sufficiently low capacitance as to not distort the D+ and D- signals. NXP also has a good application note on the subject - the note you cited also mentions it (see page 5).

Essentially, ordinary TVS arrays have sufficient capacitance to distort the edges of the D+ and D- signals, causing issues with the USBIF-mandated eye diagram test. This loss of signal integrity can interfere with communications and is a sure-fire way to fail USB certification.

Many suppliers market USB-specific TVS arrays for ESD protection. They will be rated appropriately - i.e. you don't need to worry about voltage rating etc. - just get one that is intended for USB and you should be OK.

As for the SHIELD connection, you are correct - it is the metal casing of the connector and the braided shield of the USB cable that connects so it, which is likely referenced to protective Earth somewhere on the PC side of things. For EMI reasons it should not be directly tied to the GND signal connection, but should be connected through some impedance. I've seen both parallel resistor / capacitor (as you've shown) and ferrite bead connections between them.