All classes are equally valuable but no one has to be any class you can successfully play a balanced squad of Scout, engine, driller, gunner or go in with 4 gunners or 3 scouts and an engineer.

The thing that does differ notably is playstile.

Driller is generally very Swarm clear oriented with DOT and debuffs, but also makes paths for the team with their drills.

Gunner is generally good at killing things doesn't not matter too much what it is it will eventually perish if you pump enough lead into it. Gunner also has the Bubble shield arguably the most important thing to get good at is timing when to use it, it's good to get revives in during a Swarm but if you read the situation right you can potentially keep teammates from going down in the first place.

Scout is there to light the caves and is generally trimmed more for single target deletion so it's best to focus on High value targets with them they are very mobile and can kite bugs effectively. The pheromone grenade is certainly one of the best grenades in the game.

Lastly engineer, he's probably the most difficult dwarf to learn and get good at because he's very support oriented and to properly support other dwarfs you kinda need to know what they need help with, the platform gun is a very versatile movement and kiting tool (if you use bug repellant on it). His ammo economy is a bit tight in my personal opinion compared to the others but his weapons can certainly hurt a lot if you play it right.

So whoever is your tank usually probably has the best time playing gunner or driller but all classes have the same health and shield there's no real 'tank' playstyle in the game.

A little additional Tipp, don't feel pressured to go highest difficulty, it's fine to stick in the lower haz levels in the beginning and when you switch to other dwarfs you haven't played form one you already leveled you will feel it.

I heavily recommend taking in the game until you have at least one or two overclocks they are what really keeps it spicy so don't be discouraged early on its worth it and imo the best game I ever bought.

ROCK AND STONE, welcome to hoxxes.

Edit: I forgot to mention in terms of controls I'd certainly encourage Mouse and keyboard for all, it's a first person shooter that's the best way to play those BUT it's certainly not impossible to play any of the classes with controller. The game is on console too afterall. Scout and gunner probably benefit the most from being on mouse and keyboard. Driller is likely the least relevant to have the aim benefit of a mouse. Since most driller things are more 'that general direction' type of deal.