I am sure your Eldar Harleez are going to play both ways for both your Eldar and Dark Eldar
yes they are, because the rules, fluff and models are, word for word, identical. They are, in fact, the same harlequins. I do not, however, attempt to use striking scorpions as incubi, or banshees as wyches. The harleys are always harleys. Theres no proxying involved here at all. This is what GW intend us to do.
You seem to be (possibly deliberately) missing the point of both me and prim's posts. We're not saying you should buy one of each space marine army. We're saying you should buy
1 space marine army and
use it as
1 space marine army. Don't be greedy and try to have your cake and eat it. Choose a chapter. Play that chapter, and that chapter only. Make a decision, and live with it.
no one says a thing when Mike the trident makes a Brass Scorpion...and adds it to his slaneesh army
I have no problem with Mike's Brass Scorpion because it meets three key conditions that your army proxying does not:
1) It is clearly slaaneshi. No Khorne model is that pink. ever. Thus, theme and "soul" are satisfied.
2) it is only ever a brass scorpion. Mike never says "today, its a dreadnaught". Its always a brass scorp. every time. Thus, ease-of-identification is satisfied.
3) It is perfectly legitimate to use a brass scorp in a slaaneshi army. Its in the rulebook. Thus, not-breaking-the-frickin-rules is satisfied.
Why cant I add Shrike to my 30k World Eaters..
Why cant I use Eldrad Ulthran for my Dark Eldar?
make the core the same and add things like Thunder wolves to the mix calling them World Crushers...
I can call him Edrak Ultan of the Evil Spikey Bitz Kabal, if that would help?
your whole army will be unique.
If I made an army consisting of Baneblades, broadsides, incubi, death company, all led by Ragnar, itd be unique, but that wouldnt make it game-legal.
Please remember that Seb is a new player and does not need fiddly wierd advice about proxying armies and playing "outside the box". He hasnt even found the inside of the box yet. Let him have the same experiences we did. Let him buy an army, paint it, play with it, learn from his mistakes, and enjoy the experience.