The U35 patch notes were the last time I recall seeing heavy attack resource restore figures given. (If there’s been an update to them in the meantime, I’d be happy for the link.)

Per those numbers, you should not be getting less than 2000 of the associated resource back on completing a heavy attack (unless you are using the mythic that disables this). The figures range from 2095 to 3267, depending on the weapon.

If it’s only a couple hundred you’re getting, you should probably look into logs or CMX to see what’s going on in your particular case.

Two things to consider when expecting resource return from a heavy: The resource restore is granted only when the heavy attack fully completes. Medium attacks do not grant it. A log or CMX can help you figure out whether your attacks are being held long enough to qualify as fully heavy or only medium. Alternatively, if you are using Rakkhat’s Voidmantle, note that disables the heavy attack resource restore completely.

If you’re looking for help with resources, you can take the Sigil of Haste and/or slot the Bloody Renewal/Siphoning Spells CP. Since you’re the only one in there killing the mobs, you will get a lot of killing blows to proc these CP stars.