Leveling in this game is painful experience. Good thing is that it's fun because game isn't some grindy and boring MMORPG bullshit.
Looms are OP, levels are OP as well but it's not like they fall from the sky.
Just because they are hard to obtain, doesn't make it okay.
Like I said, the rewards could be cosmetic, that is an option. Heirloomed items try to replicate "rare" items that players and trade with other players in return for gold and other goods. It doesn't have to provide raw stats, it could look somewhat better than an unheirloomed one, (different weapon skin perhaps) and that is enough motivation for someone to keep playing.
Playing this game should be a matter of fun and progression. But the progression of power / stats needs to have a finish line at some point or else it's a broken system.
Progression could continue to a cosmetic feature, where you can unlock certain titles and looks for your characters.
However, having absolutely NO level cap, is completely.. foolish to put at least.
There is no SET or BASE, it's just the more you play the more power you get, so play.. play... days, months, years, and become the most powerful soldier out there.
That is not right.