I found the same limitation that was causing me issues as well. I don't know if this is the easiest way, but in the CSV before import, I added a quick column with today's date. Upon importing the CSV, it updated the date in Airtable for that column. I then had a View in Airtable filtered by dates prior to today. That quickly filtered out the old records that I then deleted. It added a few steps, but the time savings of importing a CSV was worth the trade. I hope this helps.

@SarahLouise Jason's idea is a quick & easy way to solve this problem! If you need a fully 100% automated way of doing this, then I would recommend using Make's CSV tools & Airtable tools to handle this for you. If you're brand new to Make, there is a bit of a learning curve, but we've got a lot of Airtable experts answering automation questions (both Make & non-Make) here.