Illithidbix
Explorer
Spells known is the topic
Clerics & Land Druids get 20 spells, plus modifier bonus, plus bonus spells making over 30 spells known.
Moon Druids know 25 (more if wisdom over 20)
Wizards know 20, plus Intelligence modifier. At higher levels, can cast low level spells with no loss of spell slots
Paladins know 15, plus wisdom modifier, plus bonus spells which can make 23 to over 28
Warlocks know 15, plus 1 each of levels 6-9, and with invocations, know potentially 37 spells
Sorcerer at 15. Yes we have Metamagic which can be quickly depleted and not always useful depending on situation.
I would say increase number to 20 known spells. That is not overpowering. And still less than Lore Bard at 24
I think it's a wider problem with Prepared vs Known spell casters in 5E.
Unless they go out of their way to make their spellcasting ability a dump stat, prepared spellcasters have the flexibility of preparation AND have more spells immediately to hand than known spell casters do.
Clerics, Circle of the Land Druids and Paladins then also get their domain/land/oath spells autoprepared.
I personally think a better paradigm would be for Sorcerers and Bards to know more spells than Clerics, Druids and Wizards can have prepared, but prepared spellcasters have the flexibility of their larger pool to prepare from.
It's not a massive problem, but I feel Mearls and co' slightly dropped the ball on this one.
The sorcerer kinda gets it the worst, even if they do have a fairly good number of cantrips.
One of the few house rules I apply is that a poor Ranger automatically know Hunter's Mark, since their spells known is spectacularly bad when compared to a Paladin.