I had a 1:8” twist T3 Super Varmint .223 for a couple of years. It was a very versatile rifle. From my load notes I see that the lightest bullet I used was the 40gr Nosler BT Varmint, which I don’t remember much about because I didn’t carry on with it past the 100 in the packet. Notes say “sub MOA” thats all. I think it was fine, just not as effective downrange as the heavier bullets.
On the varminting forums you’ll read about guys using 40 and 45gr bullets quite successfully with 1:8” twist .223s.
By far the most successful bullet I used with that rifle was the 60gr Nosler BT Varmint, which would deliver very tight groups.
As usual I think its down to the specific rifle and the load development. I’ve never considered the 1:8” shooting light (short) bullets to be a problem in the same sense as 1:12” shooting heavy (long) bullets.