To be fair, those macronutrient guidelines were established not because of any special properties of those macros (give or take the nitrogen load from protein) but because when applied as a population-level intervention they encourage sufficient fiber, magnesium, potassium, etc. You can have 50% of your calories be from fats and still live a long, healthy life, and you can do so as a population (see, e.g. Crete and some other Mediterranean sub-regions in the early/mid-1900s). You can have a much higher protein intake and have beneficial outcomes too.
Your point about the sources mattering isn't tangential; it's the entire point. The reason the AMDR exists is to encourage good sources. A diet of 65% white sugar and 25% butter isn't exactly what it had in mind though, and it's those sources you want to scrutinize more heavily.
Even for red meat though, when you control for cohort effects, income, and whatnot, and examine just plain red meat without added nitrites or anything, the effect size and study power diminishes to almost nothing. It's probably real, but it's not something I'm especially concerned about (I still don't eat much red meat, but that's for unrelated reasons).
To put the issue to scale, if you take the 18% increased risk in colorectal cancer from red meats as gospel (ignoring my assertions that it's more important to avoid hot dogs than lean steaks), or, hell, let's double that to 36%, your increased risk of death from the intervention of adding a significant portion of red meat to your diet is only half as impactful as the intervention of adding driving to your daily activities.
The new guidelines seem to be better than just recommending more steaks anyway. They're not perfect, but I've seen worse health advice.