Important difference: with Paypal, the seller decides to issue the refund, not Paypal unilaterally (except in cases of alleged fraud), and the seller can determine how much of a refund to provide.
Hmm, when I use PP to refund to my clients, PP returns the fees - it's a line item in the ledger.
That cannot be true or maybe you have a grandfathered account, as paypal absolutely does not refund the percentage fee. Same with Stripe.
My account is a five year old business account. My most recent refund I issued was Aug 2019. A line item on the PayPal statement was called "Fee Reversal" for $12.46 USD
However, a read of their current policy shows it's no longer the case - so I'll likely get dinged on my next refund.