Given the huge variety of subclasses and builds available, I don't think it's that useful to worry about class representation, as long as all of the party's functional needs are being met. I mean, I've done campaigns with nothing but different flavors of clerics and we wanted for nothing, lol.
Depending on the campaign, parties will often need:
- High single target damage for bosses.
-AOE attacks for hordes.
- Crowd Control and/or Dice Manipulation to disrupt enemy strategies
- Durable frontliners to tank damage on behalf of squishier teammates.
- Charisma skills to handle social interactions
- A good range of proficiencies and expertise where needed.
- Utility spellcasters
- A variety of damage types for when you encounter resistance/immunity.
- Healers
- Buffs, especially for attack rolls, skill checks, and saving throws.
- Other things I'm probably forgetting.
But depending on the campaign not all of these things may be necessary (eg; a "shipwrecked on a deserted island" campaign might not require a face) and some team compositions can work around certain shortcomings (eg; maybe you don't need a strong healer if you rarely take damage in the first place.)
And only once you've identified what your team needs, then you select a build that will help provide that. Keep in mind that nowadays there are usually a lot of different classes and subclasses capable of doing a given job, and most builds are capable of doing a handful of jobs (and some subclasses are decent at darn near everything.)