M-Sab is a pretty interesting case since it's undeniably one of the most restrictive mons to teambuilding rn, but because of that it's so overprepared for (similarly to M-Venu mid-XY when Psychic on Thund & Lando-I, HP Flying Specs Keld & Thund, and Ice Fang on M-Gyara were standard just to beat it).
Sub CM Keld, Sub/Taunt DD M-Gyara, Specs Sylv, NP Thund, SD Gliscor, Poison Heal Breloom, CM Lando-I, TG RD Manaphy, Lum SD Chomp, EP Lando-T, Skill Swap Azelf, Skill Swap M-Gallade, SpDef Mold Breaker Exca, SD Talon, Acid Spray Tentacruel and more have either been created or have become more common largely in an effort to beat or exploit M-Sab and the playstyle usually surrounding it.
M-Sab being the face of stall just means that people began preparing for it so thoroughly that it's not as effective as what it could be (though it still is pretty damn good). Since it's so overprepared for, I think it's too early to say we should suspect it since people are usually packing more than enough answers to it on their team.
Not going to touch on Megagross since it's stats, movepool, and ability speak volumes on their own, but in terms of regular metagame trends, fast mons like Torn-T, Starmie, and Raikou are pretty godly rn. And Gengar just IS God since people only pack soft checks or answers to it that can get pressured by other threats. CM Clef + LO 3 Atks Gengar/ Wisp Hex Gengar is pretty fucking amazing atm.
LO Diggersby 2HKOs the entire metagame barring M-Slowbro, and forgoing SD for Fire Punch is pretty cool since you minimize Iron Barbs damage and 2HKO Skarm & Gengar switchins. CB Azu is a pretty amazing stall breaker which i think is better than BD atm since people are packing more water resists to take +6 Jets, as well as Unaware Clef. With CB, Azu just says fuck it 2HKOs practically all of its switch-ins. Mew isn't as solid as it was in XY, but people definitely don't pay too much attention to it while building, so it shits on a lot of balance and offense teams pretty easily. It's really hard to break if played conservatively.
I think stat passing is lame af, and Nasty Pass Celebi is getting more usage, but i don't think it's suspect worthy. I've seen GeoPass only once in ORAS, so i can't speak on it but I'll still go out on a limb and say Scolipede's Speed passing is worse since it can get up Iron Defenses to fend off priority, hold Mental Herb to stop Taunts, and can pass SDs to Lum Berry holders or Ground types to prevent T-Waves, and can pass Subs + Speed pretty easily. Even if it the receiver's Sub gets broken on entry, they still get in for free with usually +2 speed. It's so mindless and easy to pull off, especially since phazing moves and moves like Haze and Perish Song are pretty rare in the current meta.
And no retests because everything banned will def still be broken as hell, Deo-D gets Skill Swap and can get up hazards on M-Sableye, Deo-S outspeeds all common Scarfs (unless Scarf Latios comes back again) and smacks shit with crazy mixed coverage, M-Mawile can still abuse the lack of Fairy switch-ins and beat Heatran with Focus Punch, Genesect gets a free Specs / CB boosts every time it comes in and can benefit from either, etc etc.
Why are people talking about retests right now anyway? There are still some obvious suspects that need to happen, and the meta is still in the midst of change since the Gren ban..