I think if you buy from DL you are paying to insure the full cost of the airfare whether you actually need it or not. By which I mean, if for example you book with a credit card that has trip cancellation benefits, then tacking on the DL insurance is essentially paying again for a benefit you already had. For people to whom this applies, it would be worth going to an individual provider -- I will mention again Allianz because it's the one I'm most familiar with -- at Allianz you can generate a trip insurance quote putting in a total trip cost of $0. This will give you a quote with no trip cancellation/interruption benefits, only medical payments and evacuation coverage. This can be quite cheap, and was what I was doing for some international trips until recently, since I was usually booking airfare with a CSR for the 3x points and the CSR has good cancellation/interruption coverage already.

You can also go halfway, for example if you have a total vacation outlay of $2k in expenses you could put in $1k for the trip cost (or any other amount between 0 and $2k for that matter) and if you have a loss that's the limit of what will be covered, but the premium will be lower (maybe not enough to make it worth it, or maybe it will be)

Recently however with also having an AMEX Plat which has an amazing medical evacuation benefit, and the determination that my employer's health plan covers me internationally just as well as the Allianz medical stuff for the places I've been to, I've just not been purchasing insurance at all. (I've luckily never had to make a claim, but mom has had a few minor $100-$200 expenses and gotten reimbursed from Allianz with very little hassle, FWIW)

In the end though I'll reiterate that there's no one-size-fits-all here and it will depend on what CCs/policies you already hold and/or are considering, what losses you can afford to self-insure, and your personal equation for risk vs. peace of mind.