Typically this is a subset of OTel that's being compared. Almost everything (aside from Datadog's proprietary stuff) is just smaller than OTel is, which is why it's often chosen for many different needs.

In my experience, it's often folks who have experience setting up metrics or log collection with something smaller (e.g., StatsD) and sometimes for purposes with less scope, who have the most frustration with OTel. All the concepts are different, carry different names, have different configs, have different quirks, etc. There's often an expectation that things will largely the same as before and that they can carry over the cursed knowledge they had from the other toolset.