> that we know should/previously responded to ICMP,

Is there any documentation or contract that says this shall always respond to ICMP traffic?

Isn't it possible ICMP is being filtered but not DNS?

Imagine if they had misconfigured their DNS, did a ping to 1.1.1.1, and decided 1.1.1.1 DNS is obviously down despite it only potentially being ICMP traffic.

Imagine someone having issues with a web server so they show their proof of the web server being down by showing it won't connect with SMTP traffic. This is the same concept with showing a ping.

Even if the dst host is blocking ICMP, there is still value and plenty to be learned from an MTR output, even enough to show a network/route issue.