Attack Vs bulk iv. Discussion
So I was checking my team on pokebattler in preparation for a vape solo attempt and I got some unexpected results. The victreebel #3 has (a/d/s) (5/5/14) and #5 has (13/4/7) both lvl 30 with RL/SoB, and the simulation is against a HP vape with no dodging sorted by dps. Note that the bulkier victreebel with lower att stats is doing significantly better.
Digging into the simulation the picture become clear, 3/5 of the bulkier Mon got off 2 SoB when all of the higher att one only got off 1.
Obviously this is a special case and against the other 2 movesets the higher att one does slightly better. I'm not advocating to prefer bulk over att iv but the other stats can sometimes make a difference, and when they do it is a bigger difference than a few att points can give you.

Answers
IV means almost anything, the truly important thing is the level of the pokemon.
IV only means that at a SAME LEVEL the pokemon whit higher attack IV will deal slightly more damage, the one with higher defense IV receive slightly less damage and the one with higher stamina IV will stay slightly longer in combat.
Having said that, it will always be better bad iv higher lever pokemon than 100% iv lower level pokemon.
As it is impossible to always max out all your pokemons, it is preferable to capture pokemons at level 30 (ready to battle without spend stardust and saving it for the great ones) than pokemons with high IV