You neglected several different things. Trading with a large coin cost would raise a ton of protest and could potentially lead to more people leaving because of an additional pay-to-win part of the game. The PvP having no reward would make it useless for everything except bragging rights, and with the lack of potions people would complain even more. The deletion of the log out button would actually solve this on fairly well from my thoughts, with the exception of those who use multiple devices. There's also the fact that they would have to code it all and those are very large changes in the game, so while it might seem easy, its far from it.
Easy problem solve for Niantic?
Honestly , why Niantic go for easy problem solve method?
Such as
Trading? Charge high amount of poke coin from both side per trade , solved
PVP? Make it no reward at all, solved
Multi account? Delete the log out button , solved
Answers
The easier answer to trading is:
1 Free Trade Pass Per Day.
Unlimited Premiere in the Store for 100 coins.
On Trade, traded Pokemon are rerolled like they hatched from eggs.
Powered up a low IV Dragonite and now you're out of stardust? 2 days and a buddy gets you a free better one.
Does your game have a spoofer/scanner problem? Not when you trade. It's RNG all over again.
Didd you miss a legendary because you didn't play for a while? Finish that Dex!
Do you need revenue from your game? Perfect hunters will sink cash retrading the same guys into hundreds. It costs $200 minimum per hundred, but that's how whales work?