I don't even stealth in most of my Spy missions anymore because I've decided that running Enemy Radar and paying attention to where the patrols are means I can just jump past them since parkour is silent.
Pair that with ample forgiveness for setting off alarms and the only time I (as I can only speak for myself here) have ever failed a Spy mission is when I was, am, and will be getting juggled between knockdowns and/or falling down a pit until the mission times out.
And it probably will continue to be the only way until they make getting spotted and alarms going off a bigger "oh f***
