If they take 2.9% normally, 0.4% is about 14% extra in fees for every transaction you make, but disputes on a legitimate product are probably 1 in 5,000 (and Stripe will charge you a $15 flat fee if you lose the dispute which you will if it was related due to credit card fraud).
If you sell 5,000 products at $50 that's $250,000 in revenue. Stripe would normally take 2.9% which is $7,250 but now with "fraud production" they would take 3.3% for $8,250. So you've just spent an extra $1,000 out of pocket to save yourself $15 in a dispute fee that Stripe charges you. That's really steep.
If you had 66 fraud charges within 5,000x $50 transactions (to break even on fees), I would really look into why you're getting so many disputes. That's astronomically high.