Without specific charges to examine, it is impossible to compare and contrast the pontificates of St. Pius X (reigned: 1903–1914) and John Paul II (reigned: 1978–2005).
There are, however, a couple of points that can be made:
St. Pius X was quite an innovator in his pontificate, as was John Paul II in his pontificate. As but one example, Pius X raised eyebrows when he opened Communion to children as young as seven and advocated frequent, even daily, reception of Communion by the laity. We take these gifts for granted now, but in the day and age in which Pius X reigned such innovations were rather shocking.
The Church’s pastoral practice, its liturgical discipline, and even its understanding of doctrine develop over time. Just as a man looks quite different from the child or the teenager he once was, so the Church today may appear different from what it was decades or centuries before. But just as the man substantially is the same person he was as a child or teenager, so the substance of the Church continues unchanged although different in appearance.
Analogously, John Paul II’s pontificate does not look identical to that of Pius X, but that doesn’t preclude them both from being holy popes dedicated to serving the Church.
I recommend that you study more closely the issues in which you have difficulties with the reign of John Paul II. It may be that there has been misunderstanding or that there is insufficient knowledge of what the Catholic faith allows.