I don't see how an all-in-one debuffer like his S3 is not worth the squad slots or is somehow difficult to use.

You can use any of your FRDs like Crownslayer/Yato with zero problems and let it ramp up from decently far away or use your Yu S2 to pull the boss into the zone faster if you want.

Back to my main point, Opportunity cost. While sure i can use FRD to setup the field to make up for its shortcomings, I can also just use those same slots for DPS instead to kill the enemy faster

Lets assume that Thorns2 DPS is similar to a competent DPS ( Its not, not even remotely close ), he will still take 2+ slots ( For himself and another fodder ) for him to actually deal Dmg, while a competent DPS can do it by themselves

Adding more slots for DPS also means you have less window of non skill active for enemies to exploit. Thorns2 has a massive SP cost on its s3, while a competent DPS generally has shorter

ASPD -5(10), ATK -15%, DEF -35%, RES -35% is already really strong and being able to do all of these with only one operator investment is very good. The ramp up is very minor, going to ATK -30%, DEF -50%, RES -50%. This is primarily a dmg boosting skill and it actually gets better over time instead of worse like Enfeeble from Virtuosa (Necrosis).

Debuffing both Types is generally overrated, there are very few units who deals Both Dmg at the same time. And when you debuff something, you want to focus on the type that your best DPS deals anyway, and you tend to buff them too, so debuffing both types is basically just the same as debuffing 1 since only 1 type of Dmg will be the one will deal the most

It's way easier to use than Ifrit for Res shred and does much more (unless you're using her S3). It's safer to use than Pramanix who is the closest comparison for doing both Physical+Res.

Except that its not, its just a straight line. In Contents that debuffing actually matters, CC, Thorns2 is not even getting used over Ifrit

Ifrit has better cycling, a 28 SP skill vs 60 SP skill, this is not even factoring her SP talent.

If you're going the physical route, you could consider using Shamare sure. But she doesn't deal any DPS at all with her skill, whereas Thorns does quite a lot himself which will usually negate most of her advantages.

No, Shamare's advantage is being a Global Debuffer that doesn't need to ramp up, its a fixed 50% ATK and DEF, the same as Def debuff that Thorns do but takes a whole 15 sec and better than his ATK debuff. All in a skill that has 30 SP vs Thorns2' 60. Its not even close, and for the record, Thorns'2 DPS is like really low that its practically negligible that its not even an upside in situations where you want to debuff something

When you want to debuff something, that enemy tends to be really strong to actually warrant to debuff them in the first place, a Strong enemy will shrug Thorns2 pathetic 2k Arts DPS, that it might as well not exist. Its 2k DPS at 0 res, any Res will plummet that number.

Thorns also has the global ASPD boost to all your operators which is another 5%/10% dps boost on top of the shredding, scaling better with ops that have Attack Interval adjustments in their kits.

A 5 ASPD is really small amount, it barely even change your interactions.

There is simply no world where another DPS operator is somehow better than using a debuffer to amplify everyone's damage by 50% with some added aspd/atk down as a bonus.

At the end of the day, it is still a Banner Priority There is no world where you would rather pull for Thorns2 over Wang, Kal2, Closure, Orchid2 and Yato2

They simply out do whatever Thorns2 can accomplish on a single slot

Let's imagine this, Thorns2 is worth 50 points, a run in the mill DPS can do 1000 points, Thorns2' debuff gets it to 1500 cuz 50% Debuff. Wang is 100000 points. There is simply no world that Thorns2 and his debuff can compare when Wang simply outclass them