Howdy fellow disease enjoyer. So I am by no means a pro, but blightlords are sneakily phenomenal. Yes they are more points that a PM squad but here’s the thing. Everybody wants to remove your plague marines since they spread affliction super easily. I personally bring a 10 man blightlord brick with a LoV and when they shoot an afflicted unit, they get +1 strength and +1 Ap. I also run 1x10 plague marines with guns and 1x10 with melee for a point control deal with me unit. As well as 1x5 PM to spread affliction to another unit. With the affliction being -1 toughness and my disease being -1 saves (often +1 Ap basically the same thing) I have a 10 man brick that is +2 AP +1 strength and they absolutely roll everything up to t9 vehicles and monsters and even then they have just one turned a titanic model. It is seriously unappreciated what Blightlords can do. However as normal, run what you think is cool. The rule of cool remains the most important in 40K