I think that multi-classing makes the game more granular and that’s a good thing.
It means instead of the Fighter - Eldritch knight - Bladesinger - Wizard continuum, there is now a dozen different stages between them as those characters can add a bit more fighter or a bit more wizard. You can do the same for all the other classes.
It adds choice to PCs which is a good thing, but allows for a simpler characters for new players.
It is balanced. It is usually a real choice to multi-class or not. Particular in 2024 you are choosing to give up or seriously delay some good stuff now. There are a few quirky combinations (usually involving warlocks) but I don’t disavow a whole system because of a couple of options in it… I disavow those options. A lot of this depends on the level you start your characters at. It may not be a tough choice designing fresh at level 10 but at the level 2 coalface deciding to multiclass does make a difference.
Most of all I like it because it better helps me represent the character idea I have in my head. I played a rogue (mastermind) bard (college of whispers) in a recent campaign because I wanted to play an educated, support character, spy, who is fast, sneaky and had lots of tricks up her sleeve. She was a lot of fun. The character wasn’t the most powerful but she was reliable, got to do lots of stuff and positively impacted the game.