As someone who wrote a budgeting app, historical data > 1 year is a lot less useful than most folks realize. I would say at least 80% of folks never look back further than 6 months. It's not even worthwhile for comparing YoY as your lifestyle, the economy, etc change so much.
I ended up adding per-transaction opt-out roll up functionality for this reason, effectively squashing transactions into monthly and yearly budget summary transaction. Saved a ton of space with little loss of granularity.
It was so weird to me - they were paying me hundreds of dollars so that they could reference their water bill in 1987. I have my own irrational tendencies like this, of course, but still seemed weird.
If for some reason you care about your historical data enough to import it, you can add new transactions into "error" to subtract whatever part of it they are responsible for. If the account reaches zero, you can even cheat and delete all transactions.
I spent about a week defining a procedure to export all statements into CSV, converting the CSV into a Gnucash-friendly format where needed with some GPT3-authored PHP scripts. Once a month I do an import into Gnucash and the process takes at most 2 hours.
Classifying transactions is probably the biggest time sink. GnuCash's auto-categorise feature is somewhat helpful but requires a lot of manual intervention and honestly I spent a lot of time just trying to figure out what a particular expense related to (often the note on my bank statement is not helpful).
Ultimately, 2 hours per month is probably about what it took me as well. But x12 that's 24 solid hours of importing. And once you go back a few months it probably takes longer because it is more difficult to recall what particular expenses were for.