Part of the reason that Erec's actions become so untenable is because we've no longer got the thought processes behind them. He's been our guide through the story so far, but his subtle silencing gives us no choice but to latch onto the nearest point of empathy - Enide. Yet it's done in such a way as to trick us into thinking that we're still following Erec's story.
Enshrining the male viewpoint, as the desirable norm in story-telling, isn't something peculiar to the Medieval period. The Bechdel Test wouldn't exist in today's world, if movies didn't habitually side-line female characters. Chrétien's gender perspective switch would be radical if he was a Hollywood scriptwriter now, let alone entertaining a 12th century French court.
Life revolves around the heroine of a courtly love tale, but she's not supposed to participate in it. Enide and her ilk should frankly be interchangeable, not only with each other, but with a statue, or a plant-pot, or anything that our heroic knights can focus upon as they compete and fawn. The chivalric heroine could be a rock in a headdress, as long as it's pretty and pure enough.
From the second that she's placed on that horse, a flesh and blood Enide becomes an active part of the story. She gets dirty and bloodied. She falls ill under her emotions (until then a theme common only for male heroes), and the stress of her situations turns her pale. She gains a measure of control over her life, even if it's only to disobey a command to silence.
As the story goes on, we see her intelligence shining through. She evaluates the ideals of the courtly love heroine (keeping silent) against real world considerations (Erec could die), and finds the former wanting. She out-wits potential rapists and abductors. She refuses her consent in a forced marriage.
Yet all of this is disguised under the fact that Enide constantly reaffirms, mostly in thought, her belief in the idealism of female roles within the auspices of chivalry. Her actions belay her sentiments each time. But it's done so cleverly, that audiences would be cheering her on, even as she breaks every code of courtly love.
By the time we've followed Erec and Enide into the great hall of Count Limors, the subversion of the genre is no longer subtle. Limors literally yells into Enide's face all that she should attain to be or possess. He's reciting the staples of the Romance heroines - riches, a good marriage, unthinking consent, obedience, sitting on a dais and looking pretty - but we're all cheering Enide on as she resists them all.
Her victory comes not in compliance, but that almighty rebel yell that she sounds against Limors. Her defiance is loud enough to raise Erec from the dead, mustering the full force of his chivalry in defense of her choices. He trusts and falls in love with her all over again because of that moment.
Once back at King Arthur's court, Enide is again elevated to the status of venerated, pure and ideal heroine of the courtly Romances. But it's framed as something now earned. The praise of the court is all about that scream. In essence, she achieved perfect womanhood by rejecting all that the chivalric codes (and societal norms too) perceived as perfection for her gender.