Is a low IV Snorlax just a weaker version of the same Snorlax (identical moveset) at the identical level?
In other words... is a level 30 low IV snorlax just a Snorlax that perfoms as a Snorlax at a lower level? Relatively speaking?
This is the correct way of thinking. I'll give you a bit theoretical background in short. The longer version is found here:
https://pokemongo.gamepress.gg/pokemon-stats-advanced
Combat behaviour and CPs are determined by three stats: ATT (attack), DEF (defense) and STA (stamina). They are calculated in a very similar way as follows:
ATT=(Base_ATT+IV_ATT) x level_multiplier
DEF=(Base_DEF+IV_DEF) x level_multiplier
STA=(Base_STA+IV_STA) x level_multiplier
as you can see, a higher level_multiplier can compensate a low IV somehow.
In practical view, your snorlax as it is will be a wonderfull defender, sitting in the upper flours and defend pretty good.
If you want to use it as an attacker, you could think about leveling it to level 30 at least, as every point of ATT, DEF, STA helps you to get faster wins or more resiliance and thus, possibly killing more defenders with this one attacker.
