This is definitely not the right characterization of Hyatt Diamond status. It appears you have mistaken some prevalent reports of complimentary suite upgrades as a pattern or the norm. This is not the case, and hopefully some of the responses in this thread will help temper your expectations. Upgrades are at the discretion of the property and Hyatt Gold Passport T&C's are very clear about complimentary upgrades specifically EXCLUDING suites. That means that any time a property does offer a complimentary suite upgrade, it is going above and beyond. Many people like to highlight notable experiences where a property has gone above and beyond, so you might find these reports frequently. That does not mean that suite upgrades should be expected; there are thousands of Diamond stays that go unreported because there was no noteworthy experience.

Hyatt Diamond status provides for an upgrade to the best available non-suite room, including club rooms, so it sounds like you are getting the expected upgrade every time. Complimentary upgrades are based on availability of upgraded rooms, not the rate you pay.

I'm not sure why a suite on a low floor or a corner suite comprising a separate bedroom and parlor do not meet your expectations for a suite; these rooms sounds like suites by your description. If you've confirmed a suite upgrade with the property in advance, then you can expect your suite to be ready at the published checkin time, but it's also often worth waiting a few hours if the property offers a better one that is still being cleaned. Perhaps the property got the impression that a larger suite was more important to you than immediate availability. In general the front desk staff has a lot of latitude to make your stay great, and if you let them know you'd rather have a room immediately, I've never had a property be unable to find me an available room.

In my experience, complimentary suite upgrades are more likely when more than one of the following are true:

1) You are recognized as a frequent guest of that particular property
2) You are staying at a NON-resort property
3) You are staying for a short period of time
4) You are staying during a period of low occupancy
5) You are staying at a domestic property
6) You are staying at a property that is known to be generous to Diamond members (HR Orange County, Hyatt Olive 8 come to mind).
7) You are pleasant and gracious with the front desk staff

While I do stay at Hyatt properties frequently, I don't think once every 3 stays is a reasonable expectation for complimentary suite upgrades. Out of my last 10 stays, I received 1 complimentary suite upgrade at checkin, and this was on a 1-night stay during the off season at a property I've frequented before. At all the rest I received the room booked or a room on the club floor. Most of those were run-of-the-mill rooms with not-great views. I'm fairly certain this represents much more typical Diamond treatment.

Personally I am a fan of the way the GP program is run. In contrast to Starwood, where complimentary suite upgrades are included for top-tier elites (but "subject to availability"), I much prefer the confirmed suite option. That way I can ensure that I have a suite for the stays that really matter, and still enjoy club rooms most of the rest of the time. Any suites I happen to land outside of that I count as pure gravy and chalk it up to a very generous loyalty program and property management.