I don't play stall. I don't like stall. I don't particularly like mega sableye either and don't plan using but :
We already have a significant number of stuff able to break through mega sableye such as (list extracted from smogon sheet of Sabeleye in gen 7 OU) :
- Charizard Y
- Heatran
- Charizard X
- Volcarona
- sd/sub garchomp
- Kyurem B
- Mega diancie
- Clefable
- Victini
All of them beside Victini maybe are pretty common in PRO meta.
And that is, ofc without considering the UU and under pokemon that will do the job too like :
- Kyurem (regular)
- Heracross guts
- Mega Absol
- Nasty plot Infernape
- Mega Gardevoir
- Mega Houndoom
and I am probably missing few others.
I therefore personally don't understand people saying they don't have anything to answer mega sableye...