My thoughts on
Balance:
As someone who prefers to use Balance teams and has ever since BW2, I've learned that there's a defensive way to go about building these teams as well. While you can build a Balance team around a sweeper and do very well, there is a more defensive approach that I usually prefer to take. Instead of starting with a sweeper, I usually like to start with a defensive backbone consisting of 2 Pokemon. These Pokemon generally cover the majority of threats defensively and either provide crucial support in the forms of hazards, hazard control, Heal Bell, and / or Wish, or have some sort of offensive presence to keep top setup sweepers, such as Virizion and Mega Abomasnow, at bay. Once I have this defensive backbone, I like to look for a
pivot that can come in on at least some (ideally all, but that's not always possible) of the threats that the defensive core can't handle. These threats are usually immediate attackers that don't need a turn to setup to try and break through the core. So say I have Diancie + Alomomola. These two hate Grass-types and don't exactly like Magneton either. This would make Venusaur an excellent pivot since it resists Grass- and Electric-type moves and is neutral to Steel. For balance, there's two types of pivots imo. A defensive pivot that usually focuses on defense first but still has enough offensive presence to keep setup sweepers at bay, and an offensive pivot that has the natural bulk to take resisted hits and immediately threaten opposing teams with powerful attacks. Venusaur can act as both depending on the EV spread, making it a staple on balance teams imo. Once I have my defensive backbone and pivot, I'll then look for a sweeper. After finding the sweeper I want to use, I'll try to use a teamslot to support that sweeper in particular without giving up much defensive synergy. So, for Fletchinder, I would look to Flygon, Blastoise, or Hitmontop depending on if I had Spikes or if I already had a Water-type or not. The last slot, I'd look for a 2nd pivot. If the 1st pivot focused more on defense, I'd look for an offensive one and vice versa. In the end, I feel like a Balance team with a more defensive approach should be built like this:
Defensive backbone (usually 2 Pokemon)
pivot (can be more defensive or more offensive)
1 sweeper,
sweeper support (this could be a revenge killer, hazard control, or even speed control) and
2nd pivot (more defensive or offensive depending on the 1st pivot's focus)
this team shows what a more defensive-minded balance team can look like. Diancie and Alomomola cover tons of threats and provide crucial support options. Venusaur covers a lot of what they don't like. Fletchinder is the sweeper and wincon in most cases with Flygon giving it dedicated support. Since Venusaur focuses more on defense, Scrafty is used as the offensive pivot.
Threats:
Mega Abomasnow: This is by far the biggest threat to balance right now imo. Unless you're using Bronzong, Hariyama, or fat Emboar, Mega Abomasnow is usually getting a kill or putting serious strain on your defensive core whenever it comes in. Thanks to its natural bulk, Mega Abomasnow can usually come in on the defensive core rather easily and even the defensive pivot sometimes as well if it lacks a strong super effective STAB. The sweeper and offensive pivot ideally need to be able to deal with Mega Abomasnow on defensive-minded balance teams if it lacks one of the 3 specified options above.
Gallade: Thanks to perfect 3 move coverage and the ability to possibly setup Swords Dance, Gallade is a menace to most balance teams. Common defensive Pokemon, like Qwilfish, Bronzong, and Alomomola are basically setup bait for Gallade while any offensive pivot that's slower is a chance for Gallade to trade KOes. Defensive pivots that lack a way to hit Gallade super effectively or threaten it with status can also be used by Gallade to get in safely (tho it likely won't setup on the defensive pivot if it can at least hit for neutral damage)
Durant: While a balance team will usually never struggle to revenge kill Durant, it will almost always struggle to switch in. When using a defensive-minded balance team, make sure your defensive core and defensive pivot have ways to discourage Durant from switching in freely. The sweeper and offensive pivot should ideally either make Durant very predictable or make it to where it can't switch-in at all. If your sweeper can't do this, your sweeper support slot should.
Venusaur: As great of an asset as Venusaur is to Balance teams, it can also be a nightmare to switch into. Thanks to Venusaur's typing, movepool, and Speed tier, it will likely be able to always use at least 2 components of a Balance team's defensive core (backbone and pivot) to switch-in relatively freely. If your offensive pivot is slower than max Speed Venusaur, make sure that your defensive pivot can weather hits from it because Venusaur will stick around for a long time. Ideally, both your sweeper and sweeper support options should be able to handle Venusaur in some way, but your sweeper should at the very least.
Sigilyph: With an immunity to passive damage and respectable natural bulk, Sigilyph will likely be able to switch-in against defensive parts of a Balance team. It has strong coverage and can't be worn down through status, so a Balance team needs at least 2 Pokemon to immediately threaten it. Ideally, your offensive pivot should handle Sigilyph along with a member of your defensive backbone as it can't run both Energy Ball and Dazzling Gleam. For example, using Diancie with Scrafty will ensure that Sigilyph will never have a cakewalk against your Balance team since they only fall to one move and both can't be run.
Like with any other playstyle, there's definitely more general threats that have to be prepared for, but I feel like that if you prepare for these 5 threats in particular, you'll usually cover the rest of the bigger ones without really trying or meaning to.
