Where the gap comes from
Start with the base rate. For a business in the eurozone, Stripe charges 1.5% plus a small fixed fee on a European card; PayPal charges 2.9%. Even with no border and no currency in the way, a €1,000.00 payment from Germany to Spain costs €15.25 on Stripe and €29.35 on PayPal.
Then the card crosses a border. Both add a surcharge when the card was issued outside your region, and both charge it on the gross amount, on top of the base rate. On the $5,000.00 US payment that is $82.50 at Stripe and $99.50 at PayPal.
The conversion is where PayPal pulls away. Stripe adds 2% for European and UK accounts; PayPal adds 3% for European accounts and 4% for US ones, and applies it after the percentage fee, to what is left. The two compound. On the same payment PayPal's conversion alone is $142.65, against $96.85 at Stripe.
What PayPal sells for the difference is reach. Almost every online buyer already has an account, and some will only pay with it. Its buyer protection also means disputes tend to go the buyer's way, which matters if you sell services where "delivered" is hard to prove.