Sun: No good sweepers.
Sand: All sand sweepers are countered by gliscor/bronzong/bulky levitator.
Rain: Manaphy is broked. Everything else, not so much. Kingdra is decent, not great.
Dory is far easier to counter than chomp. When return for a coverage move is viable you know there's issues. Learn to carry a counter, don't run 6 EQ weaks. And try out a balloon, it really is a good item.
Um, blaziken, charizard, leafeon, haha, doredia (yes even the flower girl) tangrowth and venusaur all want to have a word with you. All the grass types have a way of making you switch except the bug. All of the above pokemon have double speed in sun except charizard and blaziken. Instead the dragon gets a power boost being able to completely obliterate pokemon that have normal resistances. Meanwhile the chicken is steadly getting faster and killing everything in one hit, yet you say sun teams have no good sweepers? (for the record i use a sun team so i actually have experience using and fighting them)