Against the High Elf Banner of the World dragon unit I would suggest dealing with it the same way any death star should be dealt with. Chaff it, then kill its support, if you are feeling confident, once the unit is isolated (meaning you have killed the High Elf bolt throwers, phoenix, ect.) then combo charge the BotWd unit.
I have found when facing Death Stars it is essential early on to plan if you are actually going to try to tackle the 'star, 9/10 I choose to avoid and clean up everything around. My game plan would be to not send my VL into the 'star, since that is the most direct counter, but isntead try to feed the 'star wolves and zombies, with the VL kills everything else :).
Even if you eventually want to get the deathstar, often the opponent will get frustrated because you are negating their big toy, begin making mistakes, and allow you to clean up the unit. Never be afraid to look at a deathstar, especially the Banner of the World Dragon unit, and say, na. Honestly, the bolt throwers and other components are essential to making the unit work, white lions aren't too hard to avoid if they don't have chaff ;).
That is my advice. If you really insist on fighting the deathstar the build isn't as important (just don't take magic weapons), instead, put as many attacks as possible on characters (I often choose heroes over lords, as they are lighter protected). It is tough to kill all the White Lions, but W2 elf characters can be some quick points with a little luck (even a 4+ save isn't that reliable). Varghiests are great for this as they have a ton of attacks a s5 which will cut through foot elves. Consider killing lvl 2s asap, as without support casters it is much easier to negate the big threats of the lvl 4.