Choice did a review of a number of credit card and stand-alone travel insurance policies a few months ago, you should be able to buy the results online, or save yourself a bit and read the relevant PDS documents online, they’re usually easy to find, but can be quite long.
Generally, the excess is higher with the credit card policies (typically $250-$500) and it can’t be reduced for an extra fee. Credit card policies often offer higher coverage for individual items of high value, like smartphones or laptops, without having to pay extra. Watch for activities that aren’t included, retail policies are often quite generous covering things like white water rafting, skiing or riding a scooter, but credit cards may not offer cover.
Credit card policies can be a significant saving for destinations like the US.
TLDR: credit card policies are usually good, but read the PDS.