Both aren't as simplistic as people paint them. Ponting is the captain but he can't control the run-ups of bowlers, the Aussies of that time were generally skirting the over-rate issue even when managed well. But in terms of what's more damaging for the game, even if they were 10 overs down, getting through 80 overs in a day is still far more than the WI used to get through at times and no-one (surely) argues they were damaging for the game. Even at the time, when the WI sometimes got through 60 overs in an entire day, I don't recall too many people calling them out for it.
The underarm was also a complex issue in some ways. Chappell was in the midst of what's recognised as an acute depression now and, well, people make mistakes. It was within the rules at the time so I guess he figured he could defend it on that basis which was also a mistake. But still, it's a bit of a stretch to suggest that Chappell did it purely to win at all costs.
This brings me to the crux of the issue I reckon. When people are under enormous pressure, they generally revert to self-interest. Chappell has certainly said as much and I think eventually we'll hear the same from Ponting. Chappell was under the pump in life in general, the game was close, etc. He simply had enough and did what was in his best interests so he could just make the situation go away and reduce the stress on him. This is what Chappell has put on the record. In short, he snapped.
Ponting, I think, also just wanted to make the situation just go away. It was a tough tour, he was under pressure from fans for team performance prior to that, he had team members who were hurting and he was under pressure from administrators because of the over-rate. I think he just snapped too and just wanted to make the situation go away. If he pushed for the W, he'd have been suspended for the first Test against Pakistan and probably been bollocked. He did what he did and whilst he still got bollocked, reckon the uproar is less than it would have been, mainly because he was on the losing side.
None of the above reasons, I might add, justify what happened and Chappell's, in my view, was the far more egregious error(s). They are, however, understandable and it just underscores what can happen to people when they're under stress. People make mistakes. Damage to the game long-term? Vastly over-played in my book on both counts.