How brutal should pitch deck feedback be to actually help founders?

I built RoastMyDeck because most founders are drowning in polite feedback.

In the last week it’s roasted 50+ decks, with scores as low as 2/100 and a lot of “I feel attacked but this is fair” DMs.

The tool simulates multiple VC-style personas and gives a score, red flags, and a fix list for the deck.

I’m curious about two things:

1. For founders: where’s the line between “usefully brutal” and “demotivating” when it comes to feedback on your deck?

2. For investors/angels: would you ever use something like this as a pre-filter or second-opinion on decks you see, or is that a bad idea?

Any thoughts on how to keep the feedback honest without making founders shut down would really help me shape the next version.