MechaPilot
Explorer
Wizards presumably get their subclass at second level because WotC tries to avoid "dead levels" where nothing is happening. At second level, fighters get their Action Surge, clerics get a Channel Divinity shtick, and wizards get Minor Conjuration/Portent/whatever. At third level, fighters get a subclass and wizards and clerics get second level spells. Moving wizard and cleric subclassing to level three would make level two a dead level.
I didn't say move the subclasses later. If WotC felts the subclasses needed to be earlier, they should have moved them all earlier.