Correct, because copies may place all copies onto the same disk.
The point of copies is belt + suspenders: you both have your typical raid protection as well as two individual copies of the file so if one copy becomes corrupted the second can be referenced.
Additionally it's useful in the case you have a single disk (like a laptop). That way if you end up with a corrupted block you can still recover your file.
PAR2 files use much more advanced error correction than simple redundancy, they are capable of compensating for errors under a much wider spectrum of data loss situations, using the same amount of storage space.
My concern would be reading the data later. Zip files are sill ubiquitous and easily supported by all major OSes (though not mobile, so be slightly careful). With ZFS, you might have to first deal with reading off old hardware (luckily SATA looks like it has at least 10 more years) and using an old OS version to mount the pool.
ZFS seems like it will be a well supported fs for decades to come to me, but in any case I wouldn't actually stuff a drive in a cabinet somewhere and have a look 30 years later. Somewhat regular checks and moving to newer media is still generally a good idea I think.
For long term storage, I would recommend ZIP files + PAR2 over an EXFAT partition