With the introduction of Bottle Caps and the effects they give, naturally high IVs are much less important. That doesn't mean they are irrelevant, though.
The short version is that you can use Bottle Caps to "overwrite" the actual IVs of a Pokemon, and make them perfect 31s for the purposes of battling. This change was likely made to facilitate tournament play, as it is no longer a time consuming chore to assemble your perfect team of Pokemon. You only have to worry about getting the right Nature, Ability, and moveset.
Additionally, it is now phenomenally easier to achieve Hidden Power of specified types. Before Bottle Caps, you had to finagle the IVs into an exact combination of 31s and 30s to still maximize stats, while also corresponding to the correct type of Hidden Power. Now, you don't have to worry at all about the value of the IVs, only whether they are even or odd. You then use Bottle Caps to cover the imperfect numbers, and are able to straight up make them all 31s instead of being required to leave 30s.
But, it has drawbacks. IVs modified through the use of Bottle Caps cannot be passed down through breeding like natural ones. So if you decide to make a slight modification to one of your team members, you must spend the Bottle Caps all over again to make the new child Pokemon have the perfect IVs again. This is then compounded by the limited nature of Bottle Caps. While there are ways of obtaining Bottle Caps more efficiently, they are somewhat of an uncommon resource that you must spend time to acquire.
Ultimately, the answer to your question is going to fall as a matter of opinion. My personal opinion is that, because Ditto is obtainable in-game and there are methods of efficiently farming them for 5 or 6 IVs, that it's easier overall to use one. You obtain it once, and you have a great shortcut to 5 or 6 IV children across all your breedable Pokemon. This frees your limited resource (Bottle Caps) to be used for Hidden Power Pokemon, as well as Legends and Mythicals, which you have far less control over how they turn out.