Okay, the lore on these things is convoluted-but-fun.

These alien vessels were provided to the Khitomer Alliance by a variant Iconian civilization that was found in a neighboring dimension, after a strike team that included an Aetherian ally helped ward off an existence-threatening attack by their variant version of the Borg. Significant similarities exist between these starships, and the Obelisk Carriers found in our own reality, though with more modernized technology and capabilities, including an even more resilient structural field, and improved mobility.