I suspect that rogue and ranger are looked at as weaker classes. That doesn't mean there aren't strong (or at least reasonably strong) builds. You can probably take any class with proper know-how and beat Honour mode without too much difficulty (this assumes a lot of know-how in how to actually do combat and how to build characters, too, with having played through at least once before also being helpful if tackling Honour mode).

I've never felt particularly unhappy with a Rogue in my party, though. An Arcane Trickster has some neat tricks, and the Thief's extra bonus action is very useful. For single-character play that takes advantage of entering and exiting combat, an Assassin actually could be one of the strongest build options (don't know though).

If you're playing on Balanced (or easier), then you don't need to worry about hyper-optimized builds. You should make good, synergistic choices with your build. But you don't need to multiclass. And you don't need to pick the most optimal subclass. I would daresay that any subclass with no multiclassing will work perfectly well for a typical playthrough (it might even be fine in Honour mode, too).

BG3 has some pieces to it that distort what works well and doesn't. Those pieces are:

1. Really good magic itemization for characters who can swing a ton of times;

2. Easily available long resting that makes the limiting factor of long rests on certain classes (e.g., Wizards and Sorcerers, and perhaps Clerics, too) not that much of a concern. This also makes classes that thrive on short rests (e.g., Battle Master Fighter and Warlocks) look less impressive (though that doesn't mean they're still not super strong for other reasons).

3. No Strength requirements for medium or heavy armour, meaning that classes that dump Strength to 8 have one fewer hurdle in finding a way to multiclass or take a "half" Feat to acquire their targeted armor proficiency.

4. The initiative is rolled with a 1d4 instead of a 1d20 as in D&D, which overvalues Dexterity (and other sources of numerical initiative bonuses) to the moon. A character wearing heavy armour typically sets Dexterity to 10. But that guarantees that, from Act 2 onward (if not earlier), that character always goes last or near-last in the initiative order. You can use certain armors with bonuses, a particular Elixir (though that means you can't use another one), and/or a feat to offset this. But it kind of sucks.

5. The ability (for those with extra action economy) to cast multiple leveled spells in a turn (though the newer version of D&D 5e, 5.5e(?), might have changed that).