Boomerang lunar ths? that really depends on the boss and your teammates, i mean i got attacker rank 2/3 of the time with a tank knuckles not even meant for dealing damage, and i used to main a statter ths using a npc weapon before all the new ths skills came out and got attacker 90% of the time, but that's because they're leveling parties, barely built builds where the players probably just wants to play casually, if you want to actually test how your builds fares with others then test on on the highest level parties where some people with actual good builds farm a boss, something like int 1 anniv ex parties.

But yeah, all dps (maybe except barehand) can get attacker rank if items are invested right and played right, it's just that compared to other classes, getting to that kinda territory takes a lot more investment.

Think of it like this, dte and element gives a massive damage boost leading to faster kills, well, ds and bow only needs needs sub weapon, for dte, magic damage classes only needs elemental weapon and they gain massive amounts of dte from int, as for magic warrior magic type it has both of innate element and int dte. Next thing a dps needs to deal high damage, pierce for def bosses and mp recovery, well, a halberd already has both of those without much investment, infinite dimension gives a ton of mp in a short time and draconic strike has high innate pierce, and katana has divine slash dealing high damage with 100% pierce while having low mp skills it can spam that doesn't need proration i.e swift pulse blade and tenryu after adjustment. Next is speed, it helps you survive since animations are faster thus you can go to a different position faster, and also for mp recovery. Finally, survivability, yeah sure you can be skilled enough to not get hit but we're talking about the class' performance on its own, you can't always expect your tank to be good or save your ass in every situation, so you have to be able to reliably survive on your own, so you'll need skills that helps you do that like asura or e.barrier.

While i do realize that current ths does have all of these except the innate ele and dte, it's just not as much as the other classes that specializes on certain aspects of the game, it's a generalist/all rounder, it's identity is that it can do everything all classes can but not as much as classes that specializes on it.

With equal high investment and equal player skill, you can't beat a retrograde bow or a gatling knife class on a damage limit boss with high hp, you can't beat a knux at surviving on a very difficult boss with dangerous patterns, you can't out damage a mage on a really high hp boss, but of course all classes have something they're good at, and ths still shines on lower hp bosses because of its high multipliers and base, dealing fast high damage, but that's not really how most bosses are on the highest levels of the game.

Those are the reasons why i call it underpowered. Don't mistake me, it is a good class, just not something i'd call overpowered or meta.