The best part of this thread is how it can be perceived to have an agenda against either series lol
This line of thinking would have you believe sequels never do well if the predecessors aren't on modern consoles. It's just not reality.
At this point, the general public seems accustomed to games being made to jump in at any point in the series, even if they are "direct sequels" (though Prime 4: Beyond is really only a direct sequel in name and gameplay, not narrative). GTA and Uncharted both saw greatly increases sales with their 4th entries, and GTA blew up further still in its 5th. Kingdom Hearts 3 edged out the original to be the best selling game in the series, despite having a notorious level of pre-existing lore to the point of it being a meme. Hell, while it wasn't in the title, Metroid Dread's announcement trailer called it Metroid 5 before dropping the subtitle, and that now stands clear above the rest in sales.
I'm not convinced this effect is real at all. The general public seems to manage to know or just not care when prior games enhance the experience, and the Prime Trilogy will likely be rather irrelevant to 4.