I don’t think I need to cover any of the main points which are done admirably above. Your comments about what I’d easier to invest in are common ones. Something I say a lot is that this is a game of resource management as much as anything.
So, fairly simple advice but don’t necessarily look to what you can build now that’s a bit better, but what you might be able to build later. In PvE you really only need, at most, 12 of each type. Building 9 Kinglers, 7 Gyarados and 6 Swampert over the course of incrementally improving your teams doesn’t make long term sense. Ultimately, your theoretical best team of 6 at this moment is perhaps one or two Shadow Swampert/Kingler backed by 4/5 Kyogre.
Perfect world, you’d only expend 6x150k dust or so (or even less if you get lucky trades) to get your best team of 6. Obviously that’s not possible because you need teams for now.
So, ploughing 50k dust or more into levelling up that third kingler from L34 to L37 because you can might help a little right now,but not really and in the long run that’s 50k dust that could go into your Kyogre once you get the candy.
Using weather boosted, any-IV-will-do stuff is the tried and tested way to fill gaps in your team early doors. Last weekend’s CD was a perfect example, 6 HC Samurott would be entirely acceptable options until you get the top DPS counters. Then invest into what will be your likely final 6-12 over time. Lucky trades and purified pokemon are also very efficient ways to build teams.
Also look at dual use pokemon, either in terms of dual types like Mamoswine or Rhyperior or those that can be PvE and PvP, master League speaks for itself but a swampert, venusaur or machamp at the UL cap will still do very well in PvE.
The age-old advice is only power up what you need, when you need it. Pokebattler is great for working out the best counters and whether investing in a counter will yield a significant improvement.