I don't think infinite "stat" growth is the inherent problem.
Implementing stat cap creates a well-defined goal, which some players, indeed, will take as the win condition for the game. Well, some won't, some might find the end-game in killing as many other players as possible and grinding that infinite stat (read statistic) instead. If your original gripe was that infinite stats allow players who play more/longer/more intensely/etc instantly kill you in 1v1 in PvP, well you will just be killed in 4v1 (look into For Honor dominion for example). People that abuse their superior stats in combat won't suddenly stop abusing their superiority if you limit their stats, they will just abuse a different one, finally ending in their superiority in lack of ethics and resorting to actual cheating if you cap everything.
Replacing stat grind with a different meaningful* end-game doesn't make a difference, as instead of a player with larger stats, you will be destroyed by a player with more relics. Removing meaning* from end-game will change the fundamental nature of the game into a different game with a win condition (get to your defined end-game). That is not for better or worse, it's just different. First video-games did not have a win condition (ex. Asteroids, Tetris) and older games were session-based (football, chess, etc). One can argue that playing a single game of chess/football/MobA isn't really playing the game, the "true" game is in grinding skill for that game.
The argument that stat caps somehow make the game "fair" or "balanced" assumes everything else is already "fair" and "balanced", as one can not balance a perfect scale on an unbalanced platform and expect the resulting contraption to be stable.
The end-game is just a "number grind". Yes, if you don't like it - don't partake in it. If you love HnH but don't like grinding character stats - come up with your own end-game, pwn 100 newbs, obtain 20 hats without crafting any, help out the fellow noobs, so you don't look like the hypocrite ("they don't play with us - what can this spruce-cap offer me?"). Don't enforce your idea that every game needs a win condition to be fun on a dysfunctional community for which it works.
The argument that unbalanced stats promote X and stat caps promote Y and X is better than Y is a question of morals/ethics and you need only look at religions in the world to see how global and self-consistent they are. I would like to believe most people "argumenting" this way are trolling, but knowing there are no limits to human stupidity, if anyone is serious consider the following. Being able to play online video game is already a huge privilege, the majority of people simply don't any opportunity to do it (
http://www.internetlivestats.com/ says about half population has "access" to the internet, it is not a far fetch not everyone has a solid enough "access" to play online games) and by some morality is unfair, so let's do our best to accelerate heat death, where the entropy is so uniform everything is exactly fair, because no place is different from another. Saying "it promotes unemployment in players", they are already unemployed, but you'd rather take away the one advantage they have over you in the name of fairness.
I think the implicit accusation of OP's friends deaths on uncapped stats is misguided, it more has to do with hardcore vs softcore audience and/or online toxicity (assuming the killer did it purely the sake of their amusement). I think the OPs problem is closer to the permadeath thread, than stat-caps.
Also I don't see how introducing stat caps alleviates the negative impacts of uncapped stats on the community. Yes, people on the "other side of end-game" might treat you better, but how is that going to promote trade differently from now? The only goods of any value will be capped ones and if you didn't manage to get it first - why would those that have capped items trade with you? Why would anyone trust you to join them if you have a reasonable chance of killing them in a perma-death game?
All this said, I agree with OPs problems. I don't spend 10 hr/day every day on the game, I simply can't. I also enjoy friendly interactions. I was also killed with my base destroyed by someone simply being bored in W9 and had a hard time starting over again. I would love more noob-friendly trading and social interactions, but with stat-caps "noob" will just be anyone below the caps. I am not interested in HnH PvP or numbers grind, but I don't petition for devs to implement an arbitrary stat-cap, just so I have an easier time defining a win condition for me.
* meaningful as in provides tangible in-game benefits