@trwnh It's not an either-or situation in AS2 / ActivityPub. context is indeed meant to allow expressing something as part of a conversation, collection, and even something specific, w/o preventing its use alongside an inReplyTo. Neither of these are singular concepts, so something can have multiple contexts/inReplyTos.
See e.g., an Article (in HTML+RDFa) using inReplyTo and context:
If you prefer JSON-LD:
curl -H'Accept: application/ld+json' https://csarven.ca/linked-web-storage-invited-expert-request