It is an error in logic to suggest that declining mass attendance and vocations are evidence that the Catholic Church hasn't changed, because of course the counterfactual is that mass attendance and vocations could be even worse had there been no changes. It's not that the Church is changing "whatever the cost", but it is definitely changing, and always has. That would not be a controversial point among Catholic theologians or historians.
Advances in science continuously force the Church to change. So does advancement in secular morality, which is continually refined and improved. Cultural norms evolve. So while it is usually many decades behind, the Church does usually eventually change to better adapt to modern society, but with every change it makes it gets harder and harder to reconcile its current doctrine with its underlying primitive ancient texts, which are of course static, for better or worse.