a "trail" bike has different needs than an "XC" bike.
Indeed. However most riders are better served by a bike with a slightly slacker head tube angle, wide bars, short stem, and a dropper post. Pro MTB racers have an abundance of experience from which to get the value of a XC bike even on terrain that most mortals would consider advanced. But a cross over athlete on their first MTB doesn't have those technical skills and will benefit from the improved handling of a trail bike even if it gives up a fractional amount in climbing or flat ground efficiency.
If the terrain you are riding makes you wonder if you could just be on a gravel bike instead, a true XC bike is probably right. But it doesn't take many semi-technical descents to tip the scales in favor of a trail bike.
At least that's my theory. The variables of rider experience and type of trail might make all that irrelevant for someone.