Steel is a terrible defensive type. That is why every one of my comments was saying that it needs to be able to perform offensively to be good. All of your arguments as for why that cannot happen hinge on its Attack not increasing. I think that is one of the most likely things to increase, now that it has freaking ice picks for hands.
And yeah, two 4x weaknesses sucks, but you're exaggerating how common those threats are a tad. Fire and Fighting are common move types, sure. But Fire and Fighting types themselves are not so common right now, mainly because of all the Fairies. And even if they were, it's not even worth implying Vacuum Wave will ever be an issue, considering nothing ever runs it.
I know the Speed is a problem, as it has to be pretty bad to be slower than regular Sandslash, but a HA may still change that. Also, Trick Room is far from a gimmick. I don't know if you played any of the competitions that have been running, but any with Groudon and Kyogre allowed were dominated by Trick Room. I myself placed top 10 in the UK with my own Trick Room team last time I entered one. And with the prominence of Dragons and Fairies in that meta, you bet I would have tried A-Sandslash on my team if it was an option. There were also several Trick Room teams in the VGC 2016 championships, so it is still very much relevant.
And, I appreciate it doesn't look good, but going that in depth with calculations is absolutely pointless when we don't know what its stats will be. Again, I am pretty sure Attack will get at least a small buff.
Steel is NOT a terrible defensive typing. It's by far the BEST defensive typing. It resists: Flying, Ice, Bug, Rock, Normal, Psychic, Fairy, Steel, Dragon, and Grass while also being immune to Poison. It takes reduced damage/no damage from over HALF the type chart! Plus, it only has 3 weaknesses being Ground, Fire, and Fighting. It's an amazing defensive typing. No, Ice is the terrible defensive typing here, and due to it having that type in combination with Steel, it doesn't work unless it's all out offensive, which looking at the obvious speed loss, it won't be. The Ice typing here hurts Sandslash TOO much. Ice picks as hands isn't evidence enough, that's an observation. What we do know about A-Sandslash is that it's going to be slower than normal Sandslash, and with an already low base 65 speed, it won't be a speedy mon' at all. With the emphasis on the massive steel-like spikes, it's more than likely losing speed for bulk, which doesn't benefit A-Sandslash at all.
Fire and Fighting are by far some of the most common types in competitve. In OU as of now(Including BL) we've got these fire types: Heatran, Char-Y, Char-X, Victini, Volcanion, Talonflame, and Volcarona. Fighting types: Keldeo, Breloom, M-Medicham, M-Lopunny, Terrakion, Hawlucha, M-Gallade, and M-Heracross. That's a decent amount, but when you look at them as coverage moves? Do you know how many Pokemon carry HP Fire, Flamethrower, Focus Blast, Fire Blast, Mach Punch, Close Combat, Superpower, Hammer Arm, etc...? A LOT. To name a few: Azumarill, Scizor, Serperior, M-Venusaur, Magnezone(Which will trap A-Sandslash with Magnet Pull), Clefable, M-Pidgeot(Heat Wave), Alakazam, Staraptor, Togekiss, Bisharp, M-Manectric, should I go on? Even if it isn't STAB, A-Sandslash won't take a hit from either move, and they're extremely common right now, and that won't change anytime soon.
What Hidden Ability would it get? Sand Rush? Chlorophyll? Speed Boost? A 'hypothetical' speed boosting ability in Hail? Sorry, but unless the latter happens, not a chance. It's more than likely to get something like Iron Barbs if it even gets a HA.
Trick Room is a gimmick. Maybe less so in Doubles, but hugely so in singles. Trick Room isn't all that reliable, especially since there's no ability that automatically activates it, and there's no item prolonging Trick Room like Heat Rock. Easily shut down by taunters, too. Also, you mention you used it. Did you see many people using it themselves while you played? That's what matters. Not because you yourself did well with it.
Yeah, hence why I said "Assuming"? Even if it gets a *small* buff like 10 points, it'll still be largely outclassed and will find itself in the lower end of the tier lists. I'm just being realistic here, I know that looking at it's ability, Sandslash's stats, info we have on A-Slash, and it's typing it doesn't look like it'll be used over an Ice type like Mamoswine or Weavile, and definitely won't be used over a Steel type like Heatran or Excadrill.
However statments like "I cannot understand how people can possibly have Opinion X" makes me tilt my head a little. Why is it so difficult to conceive that others have a different opinion? Statements like that are only very rarely a genuine wish to understand that differing opinion, more often they serve as a means to ridicule the people that hold that opinion.
It's not that 'I can't understand people have differing opinions', I don't understand why people immediately toss something new in the bin because it isn't a new Pokemon. It happened with Megas, and again with Alolan forms. Hell, we've yet to even use Alolan forms and people are already saying they hate them and would've rather had something else. In my
opinion it's silly. Happy?