I’m not completely sure which natures you are using for the first 5 mons so can’t give any advice on that so will just give other pointers.
Firstly the 252 atk 252 spatk ev spread should generally be avoided in favour of adding bulk/ speed investment (3 of the mons with 252 spatk don’t even have any special moves). So I would change these evs:
Gliscor (244Hp/ 52 Def/ 192 SpD/ 20 Spe) to make the best use of its bulk and 12% regen a turn)
We will get onto my suggestion for quagsire, and even keeping that mon the move set doesn’t work imo.
Krookodile (252 Atk/ 4 Def/ 252 Spe jolly nature) in these situations it’s best imo to put the 4 float evs not in Hp to keep the Hp number odd for rocks and spikes damage.
Excadrill (252 Atk/ 4SpD/ 252 Spe adamant nature)
Mega swampert (116 HP/ 252 Atk/ 140 Spe adamant nature) no idea what this ev spread really does but it’s the only spread I could find that wasn’t for a rain sweeper.
You only need one stealth rocker in the team which I would suggest as krookodile allowing for more coverage in the rest of the team.
Gliscor- I would just replace stealth rock with roost for more reliable regen.
Quagsire is outclassed in most situations, generally only ever being used as an unaware mon in stall, however it is clear that the team needs a water absorb ground type mon so I would suggest seismitoad for this role.
(Specs toad 252 HP/ 252 SpA/ 4Spe with hydro pump, earth power, focus blast, grass knot is a rly good anti lead imo cos everyone expects it to be the rocker)
Excadrill not running earthquake is a bit weird and so I would replace rocks with that on it, also rock slide would generally have more utility at covering excas weakness to bulky birds than x scissor so I would swap those. (This also definitely needs speed to make sand rush as useful as possible so I wld do 252 atk 252 Spe adamant nature). Also maybe use life orb for more damage.
I think running swampert mega is a bit pointless outside of rain so I would probably replace that set with normal swampert choice banded (88 HP/ 252 Atk/ 168 Spe adamant nature with waterfall, earthquake, ice punch, toxic) ik toxic on choice is weird but this is the standard band swampert set.
Running normal swampert then frees up garchomp to be mega instead so I would suggest mega garchomp (252 Atk/ 4Spd/ 252 Spe jolly nature with swords dance, earthquake, stone edge and substitute).
This team also needs a standard defensive hippowdon with smooth rock to enable all the sand synergy, I would probably replace krookodile with this cos then hippo can be the lead rocker instead.
