tl;dr: it all depends on how much risk you want to take.
It's not too hard to find pics on the internet where a blade has folded because of a disc brake. The solution a lot of people use is to put a big, long Willits-style mount on the disc side. And thus achieve the same thing as an overbuilt blade does only with less safety margin. There are other approaches that, by their reports, work for some people. Personally, I ride my bike for distances and in places where a fork blade folding would be extremely inconvenient. I am a little skeptical about the advantages of fork blade compliance anyway. The times when I have been aware my fork flexed appreciably, my hands still got a beating. And my rim brake bikes with smaller tires but more compliant forks do just about nothing for hand comfort. Tire compliance is where it's at, IMO.
I'm unconvinced that people are doing the engineering on steel forks needed to really answer the safety question. I'd rather just overbuild and not worry about it.