They are of no significance, when everyone has them. Try fighting a guy in +3 armor set and +3 weapons with an unloomed 1h, feel the disadvantage as you glance/do little damage again and again, except for perfect hits to face.
Although they may be of no significance then why does my previously unloomed military cleaver do exceptional damage. Currently its +1 but thats only been for maybe a week, before that when i was using it i was killing people in +3 milanese in about 3 hits....even general medium armour im one or two hitting.
Heirlooms do help your survive a wee bit longer but even then if your opponent is:
a) A good blocker
b) Knows melee inside out
c) Knows where to hit and with which swings
d) is a good shot with ranged
Then you basically stand no chance loomed or unloomed. Heirlooms do not make a player skilled, players with unloomed items can still thrash players that are loomed armour crutches.