I would bet quit a bit of money that the goods move around as you guess.
INNO has no need to cheat.
Between the design of negotiations, people who can't figure out optimum negotiation strategy, and most important, the only reason people buy Diamonds to begin with, impatience, there are always players who will dump Diamonds into negotiations.
The downside of INNO getting caught doing such a cheat is huge: Coiners confidence shaken and much worse, the EU frowns heavily on software companies doing such things.
Nevermind the cheat being demonstrated mathematically by the player base, that isn't proof positive.
Nor is it proof positive that it's crazy to cheat for 10 Diamonds when INNO gives hundreds of free Diamonds to thousands of competent players every week.
All it would take to ruin INNO is one disgruntled dev deciding to blow the whistle or blackmail INNO.
But I'm glad you posted, you brought up something I missed earlier:
so everything by design is made to make them money and diamonds are how that's done
Well, that ain't quite right.
Seems that INNO spent a part of their effort over the years marketing themselves to investors based on number of players, time spent in games, and number of clicks as well as their revenue, ie, the sale of Diamonds.
This worked well for the owners of INNO. The current majority stockholder bought a fifth of the company in 2016, upped it to 51% in 2017 and late last year upped it to 68%. That last purchase was for over 100M Euros giving a net value for INNO of abour 3/4 Billion USD.
From the CEO of the parent company:
“Through the creation of a new joint gaming group together with InnoGames’ founders, InnoGames’ best-in-class expertise in user acquisition, live operations and business intelligence strategies can now benefit all of MTG’s gaming vertical companies, as well as future new acquisitions.”