Join Date: Dec 2009
Location: Dallas-Fort Worth Area
Dragons and wyveryns and similar monsters are more rare in 8th edition. The greater daemons of daemons of chaos are also more rare now. The first reason is because cannons and certain other war machines (doom divers, even direct hits by stone throwers) can kill them too easily and poisoned shooting and attacks and certain magic can also take them down too easily. The second reason is that, with the new steadfast and ste up rules, certain units can tie them up and wear them down with wounds over time since a roll of 6 to wound autowounds and most monsters do not have a great armour and ward save (regen on hellpit aboms and hydras are exceptions for those units). Third, there are a lot of characters and models with high strength that can deal with monsters (including flaming attacks) that can hold up against a monster (warriors of chaos lord, a dreadlord, an oldblood with great weapon, ironguts, GW special units, etc.). Finally, large monsters eat up a lot of the points allotments either in the character categories (when mounted by a character) or in the rare slot. Many armies that ran characters on monsters in 7th edition now prefer a fighting lord and a lord mage to fill out their lord points allotment.
Whether to attack the mount or the rider depends on the situation and relative saves. A high elf dragon lord with re-rollable high armour save and 4+ ward is harder to wound and kill than a T6 dragon with minimal save, especially if you have S5 and S6 attacks. I've often won combat with static CR (banners, ranks) plus wounds on the monstrous mount sufficient to force a break test and break the lord from combat.