I mean you're right, I'm not saying that Goliath perfectly equal Giants, just that most of their cultural traits align with those of giants (and are pretty much giant-kin, and replaced Half-Giants in Dark Sun). They're made more neutral so that PCs can play them, but overall they do seem like the designers were doing a bit of "how do we make giants playable while side-stepping the size problem."
And of course, with the current rules the only way to play actual giants is if the DM allows it. Although, what you could do is have every PC play a giant (and use the goliath rules with a couple tweaks for each giant type), and just scale everything up. That would actually be an awesome campaign, a party of giants of different types out to restore Ostoria; reading Volo's now there are so many quests giants would want to do, like finding the lost capital, or the secrets to building cloud castles, and so-on.