Here's the difference.
Each of Arturia's virtual synths come with a selection of presets to get you started. Mind you, when I say 'get you started'', there are hundreds of presets with each synth, and I can imagine some people just use the presets and never actually delve into making their own sounds. Across all the V Collection instruments, there are over 6,000 presets in total.
When you buy the actual synth, you get its presets but obviously you can adjust all the controls on the synth and make whatever new sound you like.
Analog Lab technically incorporates all the synths from V Collection 6, but you can only access the presets (the same 6,000+ which come with the individual instruments). You can't get 'behind the scenes' in the same way and program the synth itself unless you have also bought the full instrument. You can tweak some controls on the synths via mapped knobs and sliders (called macros) on the Analog Lab front interface, and you can save these new sounds as your own presets, but it's nowhere near as versatile as having the actual synth.
A benefit Analog Lab has over using the synths individually is the ability to combine presets from two synths together, so you could for example be playing a preset from the CS80V and the Prophet V together, or have them spit across the keyboard.
