Bluntness is often a translation problem, not a tone problem
In your own language you probably have soft-landing phrases built in automatically. In English, under pressure, those get skipped, and a direct sentence lands harder than you meant it to.
Frame before you critique
“Can I share one thing that would make this even stronger?” Framing feedback as improvement rather than correction changes how the sentence is received before the content even arrives.
Say what worked first
“Here is what worked well, and here is the one thing I would change.” Naming a genuine strength first is not padding, it signals you are evaluating the work fairly, which makes the critique easier to actually hear.