Why can't we trigger off of Was Sent Sales Email with a template ID?

I want to trigger a nurture campaign off of a sales insight email send in Salesforce. I don't want to use subject line filters as they're too open-ended (and prone to create problems). There's only one other filter which is TEMPLATE ID. I've tried all sorts of combinations to make this work. Marketo support is scratching their heads as well (telling me that TEMPLATE ID shouldn't even be available).

Is there NO way to trigger off of a Sales Insight email without using subject filter?