Not to encourage any beef, but I am still a youngin' by comparison I think! Heh.
By the way! When I "canceled by label" (setting alarms ON by label is my existing habit already), it worked to turn off my alarm with that label.
It did also open my clock app, as discussed by the OP. However, I did not have to switch the alarm manually. The provided method of "closing" the clock app would be sufficient and a lot easier than creating AutoInput actions but only IF the "cancel alarm" didn't require the additional input.
That does appear to be a "bug" or device implementation issue for the alarm cancel to not actually apply the setting and throw the switch for that alarm to OFF.