I feel like banning Z moves would be the correct competitive decision, but also so would banning critical hits, secondary effects (Flamethrower burn etc), and a bunch of other uncompetitive garbage. In general a line has to be drawn somewhere. We're playing Gamefreak's Pokemon with some additional fan rules, not Smogon's own turn based pvp slave rancher. Where that line is can often be gray. We banned Dynamax because it's a terrible competitive mechanic that made singles awful to play. Not just awful, borderline unplayable. But Z moves? Kind of lame to lose to one when you don't expect it but the same could be said of Hidden Power, crits, full para, etc. Imo Z moves made gen 7 my favorite comp gen.I too strongly dislike Z-moves (in singles) for the reason you state, and still believe that Gen 7 OU (AND GEN 8) would have been much better if Z-moves were banned and then the tier was balanced accordingly. And I like the removal of Hidden Power for the reasons you talked about, but your post has definitely made me appreciate what the move brought to the table. Kudos.
Also, anyone have some interesting, less-used defensive mons they've found to have a niche in this metagame? Wanna try to build around some.
Perhaps not on a "the best player wins" metric, but more on the "I can run Z Hyper Beam on Noctowl and OHKO a Heatran with it" levels of wacky over the top anything is viable bullshit that was gen 7. No one here plays Pokemon because it's a good competitive game because lol no it isn't. We all play because of a combination of nostalgia, competitiveness, and our own fondness for the franchise. Smogon does what it can to make things more fair but we still have to remember that we're playing Pokemon, and getting excessive with bans makes things a bit silly.
252+ SpA Tinted Lens Noctowl Breakneck Blitz (200 BP) vs. 0 HP / 4 SpD Heatran: 258-304 (79.8 - 94.1%) -- 43.8% chance to OHKO after Stealth Rock
Bro don't take this from me.