Ignoring worked fine on Vbulletin without any resource issues, not sure why it won't work on here. This has been a nightmare for us as well on our big board. We tried the add on that blocks, but that has some bugs in it and the developer is not responsive.
How about a compromise... Is it possible to turn off "likes" for someone who is abusing the system and using it to troll someone who has them on ignore, but can still see their likes?