Actually, that vortex had not truly been created by Paragon Sea Dream. It had long existed within the Mountain and Sea Realm, a teleportation path that, theoretically speaking, could be opened by anyone in the Dao Realm. The caveat was... that the price to open it was staggering.
In fact, only Paragons could arbitrarily pay such a price. Even if an ordinary Dao Realm cultivator were to overdraw on their cultivation base, they would not be able to open that ancient teleportation path.
Therefore, most of the time the path was safe. For example, when Meng Hao and all the others used it, nothing untoward happened. However, the path was not under the protection of one of Paragon Sea Dream's magical techniques, it was merely a teleportation path. Therefore... accidents could happen.
Also, certain accidents could occur which not even Paragon Sea Dream would be aware of.