Pointless to have 10 topics running on mounts. Personally I dislike them a lot. Moving to a certain position in a certain amount of time is a feature of lineage. If you decide to go to and farm on a hard to get position, people shouldn't be able to run back after ganking you on their mounts 2mins later. They allow you to bypass a lot of obstacles overall and imho thats against the spirit of classic gameplay.
So its bad just because you cannot perma fear/kill other guys just because they are on mounts? You decided to play necro, which is certainly in top 5 OP classes on classic, their biggest disadvantage is they are human mystic, who has lowest base speed of all classes, so you have to deal with it.
Benefit of mounts? Faster movement to get on your farming spot, faster checking for enemies on big landscape spots, possible to get some time for regroup once you see enemies comming for you and you