I've seen arguments that character skins can be p2w. The first time I heard the argument, they were referring to FPS weapon skins that occlude less of the screen. There's also skins that make the character harder to see because of color, size, and dimensions (smaller stature, easier to hide around corners). There can be weapon skins who's bullets have visual effects that obscure vision.
For a PvE game the "winning" aspects apply as they do with PvP. Special purchased weapons potentially give advantages, leaderboards would be skewed, and PvE successes would increase (less repair, higher returns, less chance of failing or losing equipment).
I believe at some point, the developers and community need to agree on a middle ground for monetization purposes to keep servers paid. Skins in a PvE game make sense though someone could argue certain skins obstruct less of the screen and therefore have a PvE advantage in leaderboards. Exp boosts don't give an advantage other than less time needed to level up. Exp boosts can naturally have a downside because they would reduce the resource accumulation by the player as they spend less time than they normally would to gather resources before out leveling a zone.
I've heard prestige amongst mmo communities is common perceived factor. People do feel that reaching max level is something everyone should experience at the same pace; boosters diminish the value of all other users because there would be no way to tell who boosted to achieve the prestige of max level. As much as I can sympathize, I can't ultimately agree that a character's level has true value. Whether someone bought a max level character versus spending days/months does not truly give value in a p2w stance. A level is a number without any advantage. I can't get myself to believe exp boosts to be p2w when at the end, the player is no stronger than the others. My alternative for prestige is achievements that would be a direct indicator of time spent and valor. Badges, icons, decals, can all be indicators however that could arbitrarily create division or bullying.
I see the main p2w argument in Em8er is resource boosts. My biggest proponent for allowing boosters or benefits is for people who do not have time. When I was in school I managed to have a lot of time for games. Nowadays when games take too much commitment, I frankly don't try; the time needed plus management just to reach "the best part" of a game can be too much of a climb. On a monetization stance, disinterested players is terrible. Em8er would probably benefit following what WoW does with their Rest meter. Players who log off receive increases to their exp gain; Em8er could extend that into resource gain too. Not a huge gain, but enough to entice players who can't commit time, to actually feel like the time they do spend is rewarded enough to come back.
In closing, paying money to gain an advantage over other players in a competitive environment, either on leaderboards or PvP, is p2w. Paying money to speed things up so you can join the end content sooner but does not give you an advantage to step on top of other players in the economy or leaderboards, that's not p2w...you're not winning anything but are speeding yourself along and not harming anybody else's experience.