Best class combo for a player with less levels

[Aaedimus]

I'm entering a game where I'll be level 1, and the other players are 3. The level progression works: 1 session to get second level, 2 more for third level, and 3 more for every level after, meaning I will always be behind.

I'd like to play a caster type (Cleric, Bard, Wizard, Sorcerer, Druid)

What race/class/subclass will help me to not feel underpowered when playing with the team?

I'm thinking whatever class I choose the playstyle will probably be control and support focused.

Also, it's a Eberon campaign

[Aaedimus]

We're basically masked vigilantes being trained to replace an old retired vigilante (batman beyond style).

I was thinking of playing mine as a homeless urchin by day and trying to mix the Rorschack personality from watchmen with someone like batman's expertise in staying in the back being ready for any situation, and being in the right place enough the right till at the right time.

We played a test game, and I posted up on an upper floor overlooking the combat providing information, sniping, and situational fog clouds before sliding behind the combat to close a door, effectively splitting the enemy into two easier to manage groups. So, that's how I plan on playing

[Man_Over_Game]

With how experience scales, you'll quickly reach their level. They'll be halfway through level 4 when you're level 3, and you'll definitely be on equal footing by level 5.

Someone who utilizes a large number of tools for a large number of problems really sounds like a Bard, a Druid, or a Cleric.

Cleric would be better if you plan on being on the front lines, or if the team has melee combatants who can use your healing and buffs.
Narratively, sometimes you have to get your hands dirty, and your God respects your hard work and incentivizes you to pursue your goals.

Druid would be better if your team needs you to be extremely versatile and skilled at exploring and scouting.
Narratively, you have the need to go anywhere. Knowledge is power, and in an arms race of knowledge, you're the guy with the gun.

Bard would be better if your team needs skills focused around interacting with people and manipulating them.
Narratively, people are just another tool to use. Sometimes, you manipulate them into doing better, sometimes into doing worse, but it's never an accident.

Because of the fact that you're low level, and health/damage is the greatest difference between high and low level characters, I'd recommend playing something safe, something that's most comfortable standing far in the back.

I'd recommend playing Lore/Whispers Bard, Knowledge Cleric, or Dreams Druid.

[Rhedyn]

Well I would always recommend Fighter 1/Abjur Wizard X Rock Gnome.
For Fighter you grab defense style.

Is anything special about this build at lower levels? No, it's just a really strong build. You have plate armor, a shield, and +1 from your style for 21 AC. You also have the shield spell for a situational 26 ac. Whatever damage you do take will be taken by your arcane ward and even if you do take damage you will have con save proficiency so you can maintain some nastier concentration spells that a normal wizard might have trouble working with.

My buddy has been using the build in his "West march" groups so he has experienced level disparity, but he also has never lost a real hit point yet and wades into melee at almost any opportunity with buff spells.

[Guy Lombard-O]

With how experience scales, you'll quickly reach their level. They'll be halfway through level 4 when you're level 3, and you'll definitely be on equal footing by level 5.

It doesn't sound like it:
"I'm entering a game where I'll be level 1, and the other players are 3. The level progression works: 1 session to get second level, 2 more for third level, and 3 more for every level after, meaning I will always be behind."

I'd talk to your DM about that. Starting and playing catch-up is all well and fine, but MOG is right that you should be able to eventually catch up to the rest of the group. I've been the late-comer to a game where you weren't allowed to catch up, and it's...annoying. ExP aside, it really won't be cool for you to always feel like a bit of a sidekick to the rest of the (more powerful/higher level) group. Maybe he can merge you in by early tier 2?

[Man_Over_Game]

It doesn't sound like it:
"I'm entering a game where I'll be level 1, and the other players are 3. The level progression works: 1 session to get second level, 2 more for third level, and 3 more for every level after, meaning I will always be behind."

I'd talk to your DM about that. Starting and playing catch-up is all well and fine, but MOG is right that you should be able to eventually catch up to the rest of the group. I've been the late-comer to a game where you weren't allowed to catch up, and it's...annoying. ExP aside, it really won't be cool for you to always feel like a bit of a sidekick to the rest of the (more powerful/higher level) group. Maybe he can merge you in by early tier 2?

Ah, missed the part about "3 more for every level after". Most tables I've played at that use a Session based system base it off of your current level. So it'd take 19 sessions to get from level 19 to 20.

If these are based on number of attendance sessions, ask if there's some extra credit you can do. Maybe ask him if he can run an encounter or two as a solo event in your backstory with you that counts as attendance, or maybe you go on a solo mission during some downtime that provides an extra boost.

[Aaedimus]

We have two rogues (mastermind and arcane trickster) a glamour bard, and a fighter of some kind. I was thinking of running a Shephard druid. Dreams caught my eye, but at lower levels you just get bonus action heals, which is good but not super flexible. The cool Dreams druid effects are much later.
I thought moon druid would be nice because I get that early kit wildshape boost to help even out that level disparity, but I was always a bit iffy on that subclass because I didn't want to rely on wildshapes and felt the other subclasses offered more

[Man_Over_Game]

We have two rogues (mastermind and arcane trickster) a glamour bard, and a fighter of some kind. I was thinking of running a Shephard druid. Dreams caught my eye, but at lower levels you just get bonus action heals, which is good but not super flexible. The cool Dreams druid effects are much later.
I thought moon druid would be nice because I get that early kit wildshape boost to help even out that level disparity, but I was always a bit iffy on that subclass because I didn't want to rely on wildshapes and felt the other subclasses offered more

Moon Druid will mostly make you into a tank. Dreams effectively gives you Healing Word while still allowing you to cast big spells with your action. It's really efficient, as most people are using Healing Word anyway.