In my observation, this argument, at best, is only describing things as marginally better than pre-2010 build up. But fear not: SF is a Gold Rush town that rises and fades 10x to the rest of the nation during every economic build up. It's not "tech", it's just the way our central banking system works.
Yes, the Mission has gentrified and mid-market is a bit cleaner. But now there are widespread homeless camps, and open defecation and needles (formerly isolated to certain neighborhoods) are everywhere. And it’s not as if the Mission crime has gone away - it’s just further south now.
Property crime is up; even in SOMA, broken car windows were an occasional thing. Now it’s every day. Twin Peaks overlook is a robbery hotspot, and some guy was shot and killed for a camera up there not too long ago.
If you only ever visit the gentrified tech zones of SF, you’d be excused for thinking things have improved, but there’s no way to argue about it objectively.