Surly mono and braid under tension can be just as damaging to mr fish if it comes into contact it is unrealistic to think our catching of a fish leaves no damage whatsoever we just have to limit our own handling of the fish to my mind, I've used leadcore but don't like it but I think the issue with it is more a case of two points. 1.if snapped off it neutralises the effect of the lead making it more difficult for a fish to free itself by shaking against the lead
2. Some fishery owners are starting to mither about how lines degrade when left in the lake and it's fair to say leadcore would be a long old time for a potentially lethal snag to hang in the water.
Please don't shout at me these are my own interpretations of my reading so if I'm wrong or have mis understood then sorry in advance