A flat rate against a stack of layers
Paddle charges the same 5% plus a fixed fee wherever the buyer is, and states that currency conversion and international handling are included. Stripe starts much lower, 1.5% on a European card for a European account, then adds a surcharge for a foreign card and 2% for converting the currency.
For sales inside your own region Stripe is far cheaper: 1.52% against 5.05% on the German example. For an EU seller with US customers paying in dollars, Stripe's three layers add up to 5.09%, against Paddle's 5.01%.
What the flat rate buys is the merchant-of-record role. Paddle registers for and remits sales tax and VAT in the places your customers are, issues compliant invoices and handles many payment methods. With Stripe you do that yourself, or pay for add-ons and an accountant.
Paddle reviews businesses before onboarding and is built for software and digital products. Consulting, agency work and one-off service invoices generally do not fit; for those, a processor is the tool.