Ok, so let’s look back a few years ago, when Mccree wasn’t doing so hot.
He struggled with survivability right? So they buffed his combat roll so he could escape high damage telegraphed stuff.
This was a generally well received buff at the time, it gave players a way to make up for the hero’s limitations by using roll in a smart and efficient way. It rewarded players for knowing what positions they can and can’t get away with.
Now, after this a whooole bunch of stuff happened, and many DPS got buffs, including Mccree, who got another survivability tool, 25hp
Now, 25 hp… is the same for everyone, it won’t give you a chance for skill expression or intelligent use because it’s a completely passive thing, it’s a buff that everybody will more or less get equal value from.
And now that the charater is overturned, you decide to take away the “smart” survival buff, yet still keep the effortless, less well received one… why?
Heck, I’d say the area of his kit that needed nerfs wasn’t even survival related to begin with, but that’s a post for another time
TLDR: Blizzard seems to prefer breaking pre established stuff that worked just fine as opposed to considering that the newer changes are what made the hero… not, fine.