Unless I was having troubles getting the pins back in, not sure I'd worry a whole lot about anything other than the cracks. The curling cylinder is a BIG cylinder, and it's a rather long moment arm on the bucket pivot. It's designed to be the strongest motion on the hoe, but not necessarily to withstand the kind of use you're describing. It might just be the angle of the dangle at which you're using the thumb. The farther the bucket rotates, the less force the cylinder can put on it to bend it like that. What I'm looking at suggests the bucket was about 90 degrees to the dipper arm, where the cylinder would apply the greatest amount of force. If you're gripping stumps that hard to try to extract them without enough digging to get them out to avoide a large crater, then perhaps that technique needs to be revisited. I'd opt for another possibility being that you're putting the teeth under things and then prying by curling and pushing hard with the boom rather than digging around them more to loosen them. In a prying technique, you're typically combining the force of the boom cylinder and the curling cylinder at that pivot. It may not be a single cylinder creating the problem. Maybe a rule of thumb (pardon the pun) would be to turn a big rock into two smaller rocks somehow before brutalizing your little tractor or it's attachments. I wouldn't blame the quality of the bucket or the tractor, and you don't seem to be, albeit I'd also verify the pressure at the curling cylinder is within specifications before I damaged another bucket. That kind of damage is going to take some SERIOUS force. This is still a good observation that might save someone else from destroying their bucket. If you grind and repair the cracks, the worst I can see the pictured damage doing is making it a pain to swap the bucket because of the pin/bushing alignments. I've seen buckets in worse shape still digging, though once I see a crack like that, it's gonna be sidelined until repaired. The new one appears to be a direct replacement, so it might be a better idea to scrap the bent one and just modify digging/thumbing techniques.