Oh I definitely think there's usefulness to multiclassing. It's for those sudden character changes. Like where you are a paladin that makes a deal with the devil.
That said multiclassing does a terrible job of hybrid style characters - which is what most people want to use it for.
I understand where that perspective comes from, but I personally don't agree with it. Yes, 2e-style has the virtue that one is accumulating xp towards multiple classes simultaneously, so even though you still level up each class sequentially it feels like making progress towards both, whereas in 3e/5e style you have to alternate. I get that, but the 2e approach comes at the cost at locking in the ratio in advancement at an even split, whereas in 3e/5e style the player can choose any ratio they want for their hybrid.
Also, the "Specialist" and "Character-Defining Mechanic" examples I gave above often require dips to work, which just isn't possible in 2e-style.
To me, those extra features of 3e/5e style multiclassing are worth the price of slightly increased difficulty fluffing OOC-sequential advancement as IC-simultaneous.