On session replay, clarity if definitely comparable to an extent. Keep in mind that the tool is very fine-tuned for a more marketing use case (w/ heatmaps, analytics, etc..). On the other hand, Highlight.io will monitor the content of network requests, trace request all the way to your backend, let you inspect the DOM, report on errors and much more.
Clarity is meant for high level analytics around product usage, while Highlight is built for engineering observability (catching and debugging errors). Highlight offers network tracing, log ingest (both client and server side), and error monitoring to serve that use-case which Clarity does not.
Not trying to be contrary, just found Clarity recently and am impressed so far.