I’ve tried probably close to a dozen Specialized saddles over the years, including the S-Works Power, S-Works Power Arc, Power Arc Pro, S-Works Power Mirror, Power Pro Mirror, Power EVO Mirror, S-Works Romin Mirror, and Pro Romin Mirror.
In my experience, the Power is the widest and flattest. The Power Arc has much more curve to it. The difference between the S-Works versions and the Pro (ti rails) version is minimal but they do feel quite different. The Pro versions definitely flex a good bit more. I have the Romin Pro Mirror on my Zwift Ride inddor bike and I can flex the base with my hands. The S-Works versions all use a full carbon base plate which is stiffer and to me, much more comfortable. It’s akin to a stiff carbon sole shoe compared to a plastic sole. The flex actually makes it less comfortable. That said, the shorter Power Pro doesn’t flex as much as the Romin Pro. Either the longer Romin is just easier to flex because of the longer length, or they might not have the same base. I think the Power Pro models still use a full carbon base. Ranking all of them in shape, the Power (not Mirror) is the flattest, Power Mirror EVO second, Power Mirror third. The first Mirror got a little more curve than the original Power, but to me, the new EVO Mirror feels flatter, albeit not as flat as the OG Power. Power Arc has the most curve. I actually wish they would make a Power Arc Mirror because I love the Mirror padding but the Power is too wide and flat. Which is why I have the Romin Mirror on all my road bikes now. More curve than any of the Power saddles. My only complaint is that it’s too long. I want a short nose Romin Mirror.
So to answer your question, the EVO to me feels flatter (less curve) than the Arc for sure, and even flatter than the Power Mirror. But, it doesn’t feel as wide overall somehow. I run 143mm across all saddles and the 143mm Power Evo feels narrower than 143mm but still flat. Which I think does help with thigh rub. They also now make a 130mm version so you could try that. I still prefer the Romin over the EVO for my road bike. The EVO I have is on the gravel bike now.