You're missing the point. If your detachment is significantly weaker in both numbers and firepower than your main fleet, which by its limitations it would be, then winning that fight you otherwise wouldn't be able to initiate is less certain - especially if they decide to go full assault on you due to the time pressure.
As long as I get to pilot a ship in detachment this won't stop me (and otherwise I'll never use detachments, losing ships to autoresolve is not fun).
Player piloted Hyperion can survive against anything as long as it has CR. Phase frigates can last quite a while too. If enemy has not too many fighters even simply fast frigates like Tempest are ok.
Unless time to main fleet arrival will be extremely long (5 or more minutes), stalling (and getting quite a few kills in process) is not problem for well-piloted frigate.
And if they retreat in meantime - it's ok too. I'll catch them again (If I had enough speed to do it once, nothing stops more attempts), with less CR next time.
If the enemy can do the same to me, then it probably is never safe to use big fleets until endgame when you can afford a fleet that can kill everything.
It should never be entirely safe to use a primarily non-combat fleet without a significant escort. Your big fleet could also be entirely comprised of frigates and fast cruisers.
It won't be safe with escorts either. If enemy can cause CR drop (due to retreat) on my whole fleet, while paying CR only for small part of it's fleet, multiple times in a row - I'm doomed.