Hillary's changed positions pretty substantially as well; she was against gay marriage in 2008 and sent out mailers criticizing Obama for not being pro-gun enough. Not to mention the 1990s crime bill. Frankly I don't think she holds, or has held, any of those positions any more sincerely than Trump does his, but she's much more articulate with them...and the longer timeline makes it more plausible.
The gay marriage one is an interesting example. It's true that she hasn't supported full gay marriage until recently, but at least since 1999 she's stated that "same-sex unions should be recognized and that same-sex unions should be entitled to all the rights and privileges that every other American gets." and "be given rights under the law that recognize and respect their relationship".
While not bleeding edge, that was pretty firm support given public and political sentiment.
The mailer is also a bit more complex. The background was the presidential primary season. Here Clinton sought to highlight conflicting statements Obama had made to various groups where he both supported a ban on handguns in Chicago but then told people in Idaho he would defend the 2nd amendment. This doesn't demonstrate a changing position for Clinton, but a political attack on an opponent during an election campaign.
As for the crime bill - well I"m not certain here what you are referencing. Her husband signed a crime bill in 1994 making for longer criminal sentences and expanded the death penalty, but at the time Hillary's only role was that of first lady. She appeared to support it. Most people (including both democrats and republicans) have concluded that the harsher punishments did not have the intended effect of deterring crime or reducing recidivism. If this a "change in opinion?" Perhaps, but to counter, i) it would have been incredibly unusual for a first lady to voice an opposition on presidential policy, and ii) the general consensus has been that the crime bill did not have the effects its signatures had hoped for. Live and learn would be the message.
To me, none of these represent extreme policy changes, while a shift from being "very pro-choice" to "very pro-life" is, or being for free trade before wanting to impose massive tariffs, among many other large shifts of Trump.