I think there is a real possibility that Odium has vastly overestimated the permanence of splintering a shard. While he has done it before, what he HASN'T done is splinter a shard, then create a powerful impetus for those who draw investiture from that shard to oppose him. Add in the unique nature of Rosharan Investiture, where everything has a cognitive reflection that in some cases can literally become sentient (Spren) and he basically created a perfect storm for a shard to be, if not unsplintered, at least concentrated enough to form a perpendicularity. The Stormfather is a Spren that is also a shadow of Tanavast himself and is bonded to Dalinar through a Nahel bond. Finalize that with the surge of Adhesion allowing Dalinar to pull the three realms together and you have a perfect situation to create a perpendicularity.

There's a relevant part earlier in the book where it's mentioned by Azure that the Spiritual realm, which is where the power of a Shard generally resides, doesn't really have a concept of time or more importantly, LOCATIONS. In other words, if you can connect to the spiritual realm, distance is potentially irrelevant—all that maters for locations is the cognitive and physical realms. The Spiritual Realm is always in the right place. Odium apparently failed to move Honours power to the Cognitive realm like he did on Sel, which likely is the only reason this is possible.