'They are not much of a threat at their current speed.'
Izroth observed the movements of the Bikrosh and realized that even a cloth-type user with poor agility would be able to outrun them. However, if they were anything like the merman he faced in the Sea Palace Graveyard dungeon, then their speed once the submerged underwater could not be looked down on. This was more so considering the unique set-up of their raid group.
Unlike Blue Oasis, who went with 2 tanks, 17 damage dealers, and 5 supporters, Izroth chose to go with 4 tanks, 12 damage dealers, and 8 supporters.
Usually, this type of line-up would be frowned upon; however, Izroth found this to be necessary to overcome the Sprite Dwellings—at least for the present members of Sleeping Gardenia.