At this point stall is extremely hard to pull off
With the Aegislash ban the trio of Mega Heracross, Mega Medicham, and Mega Gardevoir has risen, and stall cannot efficiently check them
The closest there is to a check to all three of them is Doublade, but it has to either invest into SpDef and hope that Mega Heracross is not packing EQ or invest into physical defense and lose to Gardevoir
When the opponent's team has only one of those, it's manageable, but if it's paired up with something like Trick Latios/Rotom, or Bisharp, or another stallbreaker/wallbreaker like Mew or Knock Off genie-I of choice, or one of them is paired with another wallbreaker, like MCharizard Y, it's pretty much an auto-loss for stall player
0- Atk Skarmory Brave Bird vs. 40 HP / 0 Def Mega Heracross: 340-408 (109.3 - 131.1%) -- guaranteed OHKO
0 Atk Ferrothorn Gyro Ball (107 BP) vs. 0 HP / 24 Def Mega Gardevoir: 302-356 (109 - 128.5%) -- guaranteed OHKO
252+ SpA Mega Venusaur Sludge Bomb vs. 0 HP / 0 SpD Mega Gardevoir: 240-284 (86.6 - 102.5%) -- 87.5% chance to OHKO after Stealth Rock
The only one of those 3 that is harder to be with a common stall Pokemon is M-Medicham. We'll likely see stall much less lower on the ladder but higher level players who know how to counter those three will be just fine.
I assume that you are not aware that Ferrothorn is 2HKOed by a Focus Blast and thus can't switch in, Skarmory is 2HKOed by Heracross' CC after rocks and therefore can't switch in either, and defensive Mega Venusaur is 2HKOed by MGarde's Psyshock and thus can't switch in, and it also cannot OHKO with Sludge Bomb because Venusasurs don't run SpAtk on stall.
Which is why I said "high level player". If you gave a stall team to someone lower on the tier and had them counter M-Gardevoir, M-Heracross, and M-Medicham they wouldn't know that if they sacked a Pokemon to bring out Ferrothorn or Skarmory cleanly then they'd lose every time.