I can easily see a "deity" creature (such as Tiamat, Orcus or Asmodeus) with less than 30CR (though, admittedly, I probably would not go below 25), and still have a ton of spells, unique uber-weapons, and magical powers that make most mortals think, "Yeeeaaah. I'm not telling him he's not a god. Anyone else? Fine. Let's get out of here!"
With room for non-deity [if you want to call them "primordial" or whatever] creatures like the tarrasque and kraken, the leviathan or behemoth if they bring them in as such monsters, which can still be "simple" monsters which even the gods want kept locked away/don't want to have to fight. Can they, sure. But it would be an actual effort without a guaranteed success...ain'no deity gots time fer that!
QFT.
Honestly, treatment of deity stats (and the mechanical differences between gods and other cosmic entities like demon lords, primordials, etc) is such a campaign-specific design choice that I'm not surprised that it's bounced around so much across editions. You had the straight-stats approach of pre-1e and 1e (later modified to include a range of power boosts in greyhawk and then 1e MotP), which some DMs rejected out of hand in response to players treating deities and demigods like a monster manual (which, to be fair, it pretty much was format-wise). "Gods" under that system ranged from the "well, just relatively high-powered monsters" level (demon lords, Tiamat, some weaker demigods) to beings like Zeus or Odin, who were far beyond the power of PCs to defeat unless you really did generate a 60th-level party (possible by the rules but not really contemplated).
2e changed this entirely, both by setting a hard cap of 20th level in the core rules and making gods entirely statless and effectively infinitely powerful barring some sort of Macguffin; one flaw with this system was that it made the difference between "god" and "godlike" effectively infinite. Thus, demogorgon (lesser deity) was not even on the same scale as Graz'zt (a regular monster with hp, confined actions, etc).
3e made the odd decision to once again stat deities, but to use different systems for gods than for epic beings. You thus end up with gods who have stats but don't necessarily fit the CR/level system and have odd ability restrictions. Lots of people (the dicefreaks folks, for instance) played with the system to create deities (and also to up the power of demon lords, arch devils etc to match gods and provide high-epic challenges). In any case, you ended up with a system in which official stats for demon lords etc were at the top end of the challenge scale (eg demogorgon as end boss), but "actual god" stats were way off the chart and really only usable in non epic or even low epic games as avatars.
4e, IMO, had the most consistent system, in part because of the explicit definition of PC levels 21-30 as "world-changing epic/demigod" and the creation of a clear continuum past 30th to full-on deity stats at level 35 or so. Personally, I liked this system because it established some parity for deities, arch fiends, and world-breaking monsters while also allowing for mechanical interactions between gods and demigod-level heroes. You thus had four options in 4e: play stats as written and assume that 30th-level PCs, as the Heracles/Rama/Vidar of their world, can interact with and even threaten deities and planar rulers; cap the game at 20th level and keep divine beings and the like out of PC range barring macguffins; explicitly decide that the divine level spectrum is "stretchier" and move Vecna etc up a few levels (and thus entirely out of even demigod-level PCs' ability to fight); or make your deities statless.
It's too early to see how 5e will handle this but it looks to be somewhat similar to 4e; as CR 30 challenges divine beings like Tiamat are on the power spectrum, but at the top of it and functionally a capstone encounter only if 20th-level PCs benefit from miraculous circumstances. I'm fine with that.
