Sadly, there's a lot more to it than just passenger purchase experience. Codeshares, especially on award redemption, are a bit of a pain in the rear. LAN may not be allowed (by Alaska itself) to issue tickets for flight operated by Horizon, or even on certain routes.

LAN.com's booking engine for award redemption is long overdue for an upgrade, which is some roadmap for the not-so-near (not-so-far either) future. It's a totally different booking engine than the one used for purchasing full-fare tickets, which was upgraded a couple of years ago.

LAN's pricing scheme for redemption is a bit oldschool too, as it is not loaded on the computer reservation systems. Interline redemption, and specifically online redemption, depends on a lot of factors, plus a very complex realtime city-pair availability which is also influenced by the way partner airlines distribute inventory for LA

as you can see, redemption on lan.com has a lot of complexity. It works very well for itineraries that are fully operated by LAN, starts acting up when you throw oneworld segments into the mix, and behaves like a spoiled 4-year old when you add a pinch of non-oneworld interline alliances.