I wouldn't worry about accessibility around the marketing headline. Especially in the instance of a 1-second red gradient overlay. If you are determined to read it, you can wait. Accessibility is not 'one size fits all', mind it where it really matters. People who land on Stripe.com are not going to make a decision about the product based on one headline.
Looks cool, visually appealing.
I wouldn't worry about accessibility around the marketing headline. Especially in the instance of a 1-second red gradient overlay. If you are determined to read it, you can wait. Accessibility is not 'one size fits all', mind it where it really matters. People who land on Stripe.com are not going to make a decision about the product based on one headline.