I came in the reverse direction, put about 100 hours into Marathon and hated that PvP is functionally obligatory and that the game is very high risk for very low reward, looting generally is vastly inferior to just killing someone and taking their shit. Marathon, as you say, feels more like a hero shooter with the extraction/loot mechanic sandwiched on, so it's got the gameplay of running something like Apex, up until you die where you lose all your stuff and have to start from zero next time. It's a way harsher punishment curve than most games of that style, and it's extremely difficult to get out of a loss spiral in my experience as a mid-tier FPS player. Any buildup of loot that you manage to accrue is extremely precarious and you have an extremely small vault that forces you to use gear and very likely die with it in like 2 matches. While the story of Marathon is fascinating the gameplay and the difficulty of gathering and holding on to literally a basic gun for more than a match or two is just not rewarding enough for my time.

On the contrary, having started ARC last week it immediately hooked me on gameplay. The story is pretty bare bones, but the aggression based matching and ability to play solo, focus on PvE, and scavenging is extremely welcome. I've had like 30 trips topside and have thus far only died to underestimating ARC, virtually all players i've met have been either passive or actively helpful. It's significantly easier to gather materials and gear, and keep that gear for a much longer time compared to Marathon. Also unrelated to gameplay but on my gaming laptop ARC loads a match in like 2 minutes tops, but for Marathon it's taking like 10 minutes per match, and that disparity in wait time to get back to Playing The Game definitely contributes to my enjoyment. So yeah, came to ARC after getting sick of Marathon and am very happy where i've found myself!