Best of both worlds should you truly need to access it. Or are depositions also a concern?
Funny enough I just did a business law presentation on Comcast Corp v FCC (2010). Thanks for doing what you could for Net Neutrality
Whereas if the data is in a bank vault, you ask the same question and the reply is "IDK, I think it was about $50-100?"
The value in old data isn't just in pulling up a single piece of information like a magician pulls a rabbit out of their hat, it's tremendously useful for looking back and seeing how an organization and its methodology has changed and how that information can be applied to future project.
and more that a tool that every employee uses a dozen times a day
produces much more value than the same tool if it's used only by the big boss, and only once or twice a year as it's so inconvenient to use
On airgapped email archives, yes, the subpoena threat model is real too. That also happened to us because of some other dirty tricks by ISPs in the same campaign! Fake FCC submissions opposing net neutrality were being created with blatantly stolen user data; like, not people being tricked into singing a petition but just straight up identity theft. We documented all of this and pitched some state AGs on looking into it. New York did, which was awesome, but they ended up subpoenaing everyone including us! We were psyched about this overall of course since it was our idea, and they did end up finding out who did it which was awesome (Broadband for America, the umbrella lobbying group for the telcos) but it was a huge amount of work to comply with the subpoena. The retention limits reduced that burden. Another reason to have them!
I would also say that, if you do create an airgapped archive and store it in an appropriately paranoid way, you are likely to never ever bother to dig it out of storage before the SSD melts into uselessness. You'll miss the ocassional old email but not enough to go digging for it.
Then regulary exporting all the needed files, either just copy them with a USB stick and more secure would be burning CD-R's for each data transfer. And it likely helps having an exotic linux system on the laptop, so a windows USB worm won't replicate there if you use the pragmatic USB data transfer variant.