You tagged this post “bubble-hash”. Removed it as irrelevant
See: Dry Sift, Kief, Hash & Bubble?
Your mentors are misinformed…
dangerously so? Maybe (Don’t know what else you’ve picked up from them…).
vacuum first sounds safe enough… just not great for your oil
See: Don’t put extract on your stove
You’re loosing terpenes, and probably (partially) decarbing, along with oxidizing and darkening your product.
Only way to know is to test.