Disagree. You can patch up serious stuff enough to get proper help. If you dismiss as 'feel good' you probably dont have confidence to fix yourself and ride it out. Fair enough - wait for medics.
I've used Steri-strips for a nasty shin gash that did need further attention once I got off the hill, and for lighter cuts to my arm (which didn't) , as mentioned painkillers can be useful if you have a wait for medical attention, and a roll of zinc tape or microporous tape can be useful from small cuts to taping up a bandage. Also some antiseptic wipes/cream can help keep it clean particularly important for where MTBers ride.
Doesn't take much space but still need a small hip pack for rides where you may be more exposed.
I actually have the above packed into an old 3 fold wallet that I can stuff into a pocket even when riding completely packless.
I'd argue I'd rather carry something to patch a bad cut up than my bike up! What's more important. Yet every mountain biker carries a multi tool.