If gamefreak didn't want us to inject, they would have made their catching and training mechanics better.
Catching:
>1 in 100 availability for some mons
>Low probability SOS encounters
>GeoBats in fucking every cave
Training:
>All EV braces are locked behind battle points
>Worst level curve since gen 4 (yes, THAT fucking bad)
>Threw Super Training out the fucking window until lv 100, so good luck getting there
The ONLY thing they got right was pokepelago hatching and happiness. Breeding is easy, but training isn't even worth the effort anymore because in the end, it's still fucking nothing.

Then again, so little was done right with USUM that complaining about this is pointless.
TL;DR Just inject. This is coming from an ex-breed/trainerfag. Do yourself a favor and make the game fun for yourself.