I'm using a level 12 build.
A level 12 build that is significantly weaker than its mono-classed Paladin buddy for most of the preceding 11 levels.
At 12th its on par with its mono-classed buddy. Maybe an extra +1 saves for being SAD (and a short rest spammable 1st level slot), vs the Paladin with an extra ASI.
The above single classed PC has a Str of 20 by then, and a Charisma of 18, as opposed to a Charisma of 20 and Inspiring leader on the multiclass build.
Next level I get 4th level slots and spells, while the Dual class gets an ASI (and his Charisma is already maxed out). I know which has more value out of the two options.
The mono-class gets its Subclass abilities, its faithful steed (a large summoned bag of HP and an extra attack every day), extra attack, higher level spells and spell slots, improved divine smite, divine grace etc all
an entire level before a multi-class with a single dip.
With levels from 4-12 taking 10-15 or so encounters each to advance (so several sessions), that leaves the multi-class PC looking on in envy at his single classed PC for multiple sessions per level, for the previous 11 levels.
It's like the old Sorlock builds. Popular online, but in actual play pretty god awful.
The classic example being 'Lock 2/ Sorcerer 3 (yay, I have a better cantrip!) vs Sorcerer 5 (I have encounter ending spells like Fireball etc).