Saying that the SSPX position is flawed or inferior just because +Fellay, a certain % of SSPX priests, and a good % of the Faithful have abandoned it,
is like saying that a wife and children are "bad" because the husband succuмbed to temptations of the flesh and abandoned his family.
Or the Catholic Faith itself! Doesn't the Church lose members on a regular basis to other religions, paganism, etc.? Men can be tempted and lose the Faith, and they do. But there's nothing wrong with the Catholic Faith.
Foolish men might reason thusly:
John abandoned X for Y.
(IMPLIED MINOR) But men always choose the greater good over the lesser good.
Therefore X must be inferior or flawed in some way.
BUT THE UNSPOKEN MINOR IS FALSE!
Every sin is a man foolishly pursuing some lesser good (pleasure, etc.) over a greater good (doing God's will, holiness, being worthy of heaven)