im the kind to think everyone deserve a chance and with breath ascendence , ive learned those runt that take forever are generally those that will give you most of the unique pheno that everyone crave for and generally when you take clone they seem to grow faster than starting from seed , if you got space let them do maybe there a good surprise
I've found the opposite to be true. In my experience they are low-yielding, herm-prone, and don't match the quality of the normal/healthy seedlings. I have a 4000 W multi-strain flower room, and I'm selecting phenos with that in mind. Slow growing runts and mutants screw with the schedule and end up taking space that a better performing plant could use.
I'll give them a bit of time, but if they continue to show leaf mutations and lag significantly behind the other seedlings, I'll give them to a buddy. I can always get a cut back in the rare chance that one turns out to be a winner. I've been popping beans for 25 years, and regret growing out the runts/mutants 90% of the time that I've done so.