1. With Star Engines, their first turn mobility is better than bikes.
2. Individual Warlocks are protected by the Wave Serpent if Ordinance or other stupid things should fly at them.
3. The point cost is much lower.
4. I don't have to buy $300 of Jetbikes and convert them and find place for them in my transport.
5. More heavy weapons on the table, as well as vehicles that can contest objectives.
Now, even with Wave Serpents, the point cost of a solid Seer Council is very high. Farseer and 7 Warlocks comes to about 330, and the transport (as I run it) is another 135... for a grand total of 465. That is not a cheap unit. And I like taking two in my lists, so...
I've been scrambling to collect Warlocks so I can try this stuff out. So far I have 15 and will get three more tomorrow. That should hold me.