Pre the patch, you could expect 4.66 gems per collect if you had all kingdoms levelled.
Now, with all Kingdom levelled to 10, plus all at Power Level 3, you would expect 2.99 gems per collect.
So, yes there has been a significant reduction. One of the Dev’s indicated that GoW felt too much was being given away too easily previously, so I wouldn’t hold your breath on it re-increasing any time too soon.