Main DPS are generally the primary source of damage, and their kits often don't involve anything but damage. Their sonata choice will most often be their respective element, but can also be 2/2 element/atk or full attack.
These resonators will often have similar stat spreads to your main DPS, but have the added responsibility of buffing or making up for any team deficits. Enhancing elemental or attack-type DMG, ATK or ER, allows the Main DPS to focus solely on DPS related stats (most notably, Crit). Their sonata choice will often be Moonlit to provide additional buffs. Usually their loss of personal dmg makes up for the Main DPS's buffs, but you could consider building with an elemental set and spreading field time between the two. The stat spread and ideal numbers will look the same on either set, but it's a question of 12% DMG + 22.5% ATK on your Main vs +40% elemental dmg to your sub).
A support is exactly that; providing support to your team--heals, shields, energy, buffs. While you can always consider damage, a support's damage is often not the forefront of their build. Their sonata choice will usually be rejuvenating glow to enhance team attack. Moonlit only applies to next person, so there's little reason to have more than 1 set in a comp. Rejuvenating does not stack, so there's no reason to have more than 1 set in a comp. Rover can only run Rejuvenating at S4.
Synergy is about understanding where the primary source of damage is coming from, and enhancing that. For example, if running a resonator like Jiyan, which pulls the bulk of damage from RL and HA, using a BA buffer like Sanhua doesn't synergize well. Jiyan doesn't use BA to gain significant damage. Instead we'd consider Mortefi, who buffs HA, Aalto, who buffs Aero, or Yinlin/Jianxin, who buff RL. Or even Yangyang to support ER.
There's no elemental reaction system, so same type teams do not necessarily need to apply and have no external benefits, other than sub-DPS units that buff an element specific damage (e.g. Aalto or Danjin).
It is also for these reasons you could build basically any sub-DPS as a Main DPS; find their main source of damage, and pair with a team that enhances that primary damage. With kits intended to be a "sub-dps", the resonators will likely not have the same damage potential as one that is solely dedicated to DPS, and some of their kit may even be wasted, but if built correctly you can do (almost?) any content just the same. On the reverse, kits focused solely on damage (i.e. Main DPS kits), may not work well as a sub-DPS through their kit alone since they do not provide buffs outside of a sonata set.
Don't let the boring old meta define how you play and who you play with.
Not going to talk about specific character rotations, there's plenty of guides talking about the specifics of any given character, but let's talk team rotations. In most cases, we'll see a cycle of using the team support, applying buffs, intro/outro into the Sub-DPS, sub-DPS doing their rotation and doing their burst window, applying buffs, intro/outro into the Main DPS, applying set bonuses, echoes, and finishing off with your main burst window. Then we swap back to the support, and repeat the process. Not all fights (many overworld fights will not) require more than 1 rotation, in many cases you probably won't even do a full rotation. Based on your team, your rotation may vary based on kits and timing, but rotation through the roles in order to maximize your main's damage is the foundation for team rotation.
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