The only issue that came up with St John of Kronstadt that would have any “merit” was his relationship with his wife.
It is simply not true, however, that he married to obtain a parish position. He married because that is the rule in the Orthodox church - those who wish to serve in parish positions MUST be married, if not, they become monastics. (And when a priest’s wife dies, it is often the case that the priest will receive monastic tonsure).
This issue was looked at by the Russian Synod very closely (John of Kronstadt was not only wildly popular among the laity, he was appointed a chaplain to the Tsar himself). They pronounced in his favour and I don’t have the details, but take the Synod’s decision at face value.
That a number of his followers did some unorthodox things - this was all without his blessing and approval. He was a miracle-worker and thousands came from all over to hear him speak, and to receive his blessing. I myself met a very old Russian lady whose father was cured of cancer by St John of Kronstadt while the holy man was still alive.
The Old Believers are also strongly against other Saints, such as St Dmitry, Metropolitan of Rostov, who was an uncompromising enemy of Old Believer practices and wrote much against them, their two-fingered Sign of the Cross and the like. St Dmitry, as a Hierarch, had the responsibility to warn people about those the Church considered schismatics, and so he did. St Maria of Paris, a Russian nun who died at Ravensbruck, wrote an article questioning the Old Believer’s views as well.
Alex