All else being equal, symmetry is desirable.
However, I think the needs of the particular class can theoretically justify symmetry breaking.
On the other hand, I don't think avoiding a "dead level" is a strong enough reason in itself to justify symmetry breaking.
I see no reason the ranger shouldn't have the subclass choice at level 3 and get spellcasting at 2 rather than vice versa. This has the added benefit of making his spellcasting table the same as the paladin's, which is nice all else being equal. I don't believe that the ranger is so delicately balanced that this rearrangement will be problematic.
The mage is interesting, in that they hint in future versions you'll pick one sub-class (e.g., wizard) at level 1 and a sub-sub-class at level 2. Moving the latter to 3 would create a "dead level", and since rearranging the spellcasting table WOULD cause balance issues, the only options I see for filling it are adding a new feature or moving esoteric knowledge from level 1. (In the latter case, I think the level is still "mostly dead" or "slightly alive".)
The problem with the cleric is that while you can be a generalist wizard, you have to be a cleric of something. Unless maybe your campaign setting has an unusual arrangement between the various religions, you presumably have to pick a deity at level 1. Domains and deities may have a many-to-many relationship in the setting, but the choice of deity would still affect which domains you can pick at 3. Effectively, you'd be having players pick domains at level 1 and work backwards to select a deity that offers it, then wait 2 levels for that to matter. If that choice at first level makes no mechanical difference except to narrow your later domain choice, I think splitting the decision makes it unnecessarily complicated, symmetry or no. That choice could be made more meaningful, as presumably, wizard and sorcerer and warlock will be, but I think in the case of the cleric, that would be adding a lot of complication mainly for the sake of not breaking symmetry.
The paladin may have a similar problem, depending on what form the other oaths take. If, as in the previous packet, one of them is blackguard, presumably that choice is made at level 1 but doesn't take effect until level 3. I don't think that's as bad as the cleric's issue, but I'd still prefer to break symmetry in that case and put the oath at level 1.