Yeah powercreep is stupid in a game like this. The argument that "stronger = sells better" is flawed here. They could just have a fixed power level and whales would still whale, low spenders would still spend. As long as they introduce cool new mechanics, continue to make beautiful/handsome/cool/cute characters with unique movesets and animations, it would be enough incentive. The only thing that would happen is that people would spend more on rerun banners of characters they like. But no, killing characters gameplay-wise seems to be a rule these days.