The warning isn’t clear when it’s just text. So many text warnings say “Extreme” and the mission turns out to be relatively easy compared to what we were expecting, so it’s that threat severity warning (for me at least) goes 100% ignored, because I find it unreliable and misleading.
My favorite solution to convey information to players in video games is through demonstration. Imagine a mission where you find the ancients for the first time fighting another enemy. Perhaps one hoplite vs. some raiders. You can see what the Hoplite can do to a human target before they ever target you. You still have a mission requiring you to kill raiders after they manage to take it down, but you get a glimpse of what you’re going to be up against before actually finding yourself overwhelmed by something new. If there were scripted in-mission events that could happen, I’d suggest starting the mission on the enemies turn so that it begins with the hoplite attacking them so that you’re guaranteed to see what it is capable of.