No, restic doesn’t have this issue. The problem is in a Kopia’s implementation - they heavily relay on unlimited prefixes, which causes much more list requests and forced the gateway to decrypt paths then order them and this consumes a lot of resources.
If the paths are not encrypted - they already ordered, so no heavy load on the gateway. The same would happen if Kopia will use the limited prefixes (“folder/” vs “folder”), but they decided to make it wrong.
restic would work much better. You may also try to use Duplicacy: