The gust is assumed to produce a change in angle of attack, a positive gust increasing alpha. If you are heavy and flying level at 4deg alpha and the gust adds one deg, which is a 25% increase in lift, or 1.25g. If you had been light and holding 3 deg alpha for level flight the gust would give you a 33% increase in lift, 1.33g. If you are measuring gust effect by g, as you do, then light is bad, heavy is good.

Imagine a really heavy aircraft flying with the wings flapping away but the fuselage just steaming along

This brings in another issue.

For the heavy aircraft, the stress at the wing attachments will be higher and it will use up fatigue life faster. So for long fatigue life fly smooth and fly light…