** This is a comment, since I cannot seem to post one against the answer using edge, I had to post as an answer **
Hi @Navtej Singh Saini - thanks for your response. After reviewing it, I understand you are referring to the scenario where the customer keeps a read replica of MySQL in secondary and then basically promotes it to primary in the event of a disaster. I understand that a capacity concern will not come into picture when this option is chosen, as the replica is already provisioned. Definitely a consideration we have in mind. However, the client sees this as a premium option - i.e. a Hot DR where the secondary is always provisioned and they pay for both the compute and store.
The question is more about the other option, i.e. a MySQL database provisioned in the primary with only GRS backup (with no replicas in secondary), so we pay for storage in the secondary region and hence, there is a need to provision a secondary instance when disaster strikes the primary. We understand the time to provision a MySQL instance and attaching that to GRS backup is part of the RTO - that's all good. What we are after is if there are any capacity guarantees in the same line as ASR.
So essentially we are trying to understand the trade-offs, after all architecture is a business of trade-offs :). If there are really no additional guarantees of capacity in the secondary because the impact was on an outage of primary (which is something ASR seems to provide) - we will probably go with the read replica and the additional cost will be well worth it, but we do want to ensure we've understood our options before making that decision. Any further clarifications will be sincerely appreciated.