Few things. Firstly, while I kinda understand the Steel-type comparison ish (it's not that good tbh 'cause these were for when they were important elements of defensive synergy), my key issue with it is that the stuff that ran Shed Shell for Gothitelle weren't Steel-types and weren't usually defensive. Like, the key thing here is that it removed key offensive threats to m ake stall extremely hard to take on short of packing multiple stallbreakers on one team. Secondly, noone in their right mind is trying to trap a U-turn user when you could be trapping shit like Manaphy, Togekiss, Heatran, Amoonguss, Chansey etc. that you actually win vs. The variant used in ABR stall ran 128 HP IIRC. I can't remember what it does exactly, but I do know that one thing it achieves is avoiding a Seismic Toss 3HKO. I also know that Gothitelle wasn't used for it's offensive presence, but rather it functioned by PP stalling it's targets or just crippling them with Trick which means that it's low SpA stat didn't matter that much in the long run (that and it was also able to score free CMs vs. stuff that it's PP stalling if it carried the move). Outside of playing like complete ass, Gothitelle will do it's job in a matchup where it is needed, and even just having the ability to revenge kill things similarly to Dugtrio (which, for reference, has a whopping 1-point attack increase over 128 SpA Gothitelle) meant that it was able to not be complete dead weight in matchups that it didn't need to PP stall or cripple stuff with Trick, and it had utility on offense for it's ability to create setup opportunities for teammates similarly to Wobbuffet's Encore too. It didn't need amazing stats when it has passable stats and as perfect a movepool as it had for it's job, and it isn't taking on half the crap that you are referring to as it's problems in the first place. Like, seriously this thing is consistent idk why you have it in your head that it "is not near as consistent as a lot of people are implying"
Is because is the truth, that is why I have it in my head, first and foremost the Steel type Shed Shell comparison, or the Air Balloon one for that matter, is just too point that a mon running an item to have a better matchup against things that usually check it is not enough argument for something being ultra impressive, since it happens with other mons as well.
Uturn and Volturn matters because unless it is after a teammate is killed you cannot ensure your opponent is not switching too, and after one of your mons is already killed there are a good amount of times that your opponent's mon is already setted up and doesnt care about Gothitelle, a prominent case being CharX who was very popular the time Goth was allowed, which made Goth reliant on prediction on actual matches, this is especially true for Gothitelle who has a crappy defensive typing since it cannot come in freely all the time unlike something like Lando-T.
You are comparing Gothitelle to Wobuffet? They share the typing and ability, but they are worlds appart my friend, Wobuffet can come on a Xerneas using Geomancy and kill it, in short words the burden of needing to predict is muuuuuuch way less because this applies to almost any mon trying to set up , I want to see Goth when it was around switching into a CharX using Dragon Dance to see what it can do.
Gothitelle struggled against particular threats in OU much more than you realize or wants to admit, Latios doesnt care about Trick mostly, Lando-T, Gengar, CharX, Talonflame, Azumarill,etc. were incredible difficult for hear to deal with unless send out at the same time, since they could set up on the switch and kill, those ones are just asome at the top of my head I can think of.
There was a reason why this thing did not make it at the top of the viability rankings, sure when it gets going it does its job amazingly, but other mons where much more consistent at checking specific threats, others also served as blanket checks for a good portion of the meta alongside providing hazard control, hazard setting, offensive potential, defensive synergy, and so on.
Also not that it matters, but strictly speaking about offensive potential, Dugtrio is better than Gothitelle, not because of the 1 point increase in attack that you blatantly try to make fun of, but because it has a much better main offensive move(Earthquake in case you are wondering is better than Psychic), also it has 10 more BP, coupled with a much better offensive movepool.
So yeah, it can be extremely useful, and on a right prediction you reward is considerably higher than what other mons provide, ironically it also fitted well in Voltturn cores, but thing thing is not near the level of the top threats in terms of centralization and derpness.