Don't get me wrong, rain abuse physical kingdra is way better than anything a crit set could do
But the point of crit is to ignore the sp atk drop. The set you mentioned only gets to drop draco meteor once. The sniper crit set deals more damage and can keep firing them off.
Perhaps sticky web and a few more spd evs will negate the need for agility as secondary set up.
When looking at this set, don't think of focus energy as some gimmick set up move. Think of it like a one time use nasty plot that prevents sp atk to decreasing.
Scolipede can boost and pass all in one, but the problem with getting a crit set working is that; all the Pokemon that are part of the set are susceptible to priority making it a weak opening strat where it would best benefit from the initial momentum, while in late game there are arguably better boosting options. That said with the nerf to weather I think Critdra is one of Kingdras better late game sets, it can't rely on SS to be activated anymore so trading sweep potential for raw unmitigatable damage seems like a good way to go with kingdra.