I dont think that subclass design favors multiclassing per se. Yes level 3 is strong power dip etc. But this would not need to be.That said, I struggle to understand why there is such a push in favor of the subclass design, which incentivizes multiclassing.
The problem which incentizes multiclassing is again inconsistency. 5e has a really really inconstent power curve.
From level 1-3 the power of a character in 5e increases by a factor 3!
From level 3 to 5 the power doubles.
Then from level 5 to 9 or so (dont have the exact numbers) power doubles again.
When you compare this to other games there (intended) power curve is anlot more consistent.
In 13th age and PF2 (and I think d&d 3.5 theoretically, but would need to check) power doubles exactly every 2 levels.
In D&D 4e power doubles every 4 levels.
Of course a lot of power in 5e also comes from hp scaling more extremly (more than doubles from level 1 to 3), but still there is soo much power in the first 3 levels compared to later levels, which incentizes multiclassing.
On the other hand why subclasses are pushed is another one: Tjey are really really easy to design (in 5e).
Its soo much easier to do homebrew in 5e than in 4e or pf2, because its just a lot less work. You can create different feeling characters with like 4 levels with 1-3 features.
Similarily its sooo much less work to make a subclass for an existing class rather than a new class, especially since you need 3+ subclasses when making a class.







