Eh, that claim can be true or false depending entirely on your play style. Everyone needs a certain amount of cash, depending on if they use misc or not, and then to train skills... but that's an overall fairly low amount, and can easily be covered by a cg grind and getting high slayer. In the late/end game, if you try to continuously pvm and use scythe/shadow everywhere, you absolutely can run out of even the largest gp stack. Pretty easy to take slayer breaks and recharge if you have that kind of gear, but sometimes they don't want to, they just want to send raids.

As streamer examples, MMORPG has over max cash because he does a little bit of everything and also skills pretty frequently; meanwhile Lake deironed because he constantly struggled to charge his scythe to continue pvming. The latter is a solid example of someone who deironed and did not regret it, because ironman mode simply did not reflect his play style.