Looking for broader perspectives and pointers to dig deeper into this line of thought - How does Pinot compare with Elasticsearch aggregations? Can it be a good replacement the latter? [Context - I'm assessing options to build an near real time analytics engine for 10s of petabytes of mutable data. Druid and Clickhouse in the basket as well.]

Yes, there are successful migrations from Elastic to Pinot. You might find this useful: