With charge attacks, I don't feel they should go off automatically once ready. That's not to say it should remain indefinitely until you're happy to let it land, but I think there should be a timing involved where once it's fully charged, depending on the initiated skill, give it a set window of time before it goes off automatically A fighter for instance that tends to have a lot of strength may be able to hold a charge the longest (ex: up to 10 seconds) but not indefinitely, while a rogue or bandit may hold a charge but only briefly (ex: up to 3 seconds). And a mystic (haven't touched mystic yet) might have a time window in between since they're not physically all powerful, but they are a master of their craft (if they have a charge attack, maybe 5-6 seconds?).
With an auto-released charge-attack there's still an aspect of timing - it's just easier because now the thing the player is timing for is when the full-charge comes out, rather than for when an enemy comes within range or interspersed with dodging/parrying. There just isn't that much of a benefit of having a high burst-damage attack require that timing when it's realistically only going to reach a small part of the entire arena.
In contrast, for skills instead of the dedicated "heavy attack" button, that's an entirely different matter - those I think SHOULD have some abilities that have the option to hold, because things like the Deadly Dash fighter skillhave elements of optimizing their DPS by maximizing how many targets you hit with it. Makes a lot more sense for maintained charge attacks at range as well for similar reasons, combined with the requirement to aim.