Severity first is the right order: otherwise a failed-payment ticket waits behind a polite feature request just because it reads calmer. One line worth hard-coding before any tone work: anything that mentions a charge or a refund goes to a human, never to an auto-reply. Where do you draw that line in your triage?
Own severity, I'd say: a chargeback arrives with an evidence deadline set by the card network, while a refund request can wait a few hours. Same human-only gate, but it goes to the top of that queue with its due date written on the ticket. Do you pull that date from the payment processor or let the agent read it from the dispute email?