Cloudflare has tools to prevent too many form submits. You can specify which page, how many submits and so on.
I found out about this when I had a problem of somebody running a script of trying different credit cards over a two hour window.
My payment processor told me I should prevent these types of things. So I investigated and never had this problem anymore.
Cloudflare is amazing at preventing all kinds of attacks. I love Cloudflare.