Unfortunately, we do not know how powerful jotunn magic could be, since we only see glimpses of the Casket’s power (worldhopping, freezing stuff), and the present-day jotunn ice manipulation we see is after a millenium of devastation and probably lost art.
I think that the jotnar we see with the ice blades at first are doing level one stuff; note that the ice never detaches from their bodies, and the blades are very erratically shaped. Then there are the jotnar who jump into the fight after, ‘at least make it a challenge for me!’ These jotnar are capable of throwing ice chunks as missiles, creating ice pillars and ice spikes; they are better at it. Laufey is probably either at their level or above it, being that he can send magic through the ground, raise himself on a platform, and create ice weapons that are not fused to his skin. However, much of their expertise has probably been lost.
Odin’s monologue shows jotnar standing on ground that glows slightly, and the rocks around the throne also have a hint of shimmering light. This may well be an effect of jotunn magic.
The possibilities, with what we know of it, are fantastic. They could, perhaps, create a ship of ice, that either glides along the surface or actually parts the ice in front of it. Fighting them on home territory would, presumably, be a nightmare as fortifications are flung up behind the fleeing jotnar in seconds. Perhaps their greatest places always shimmered with magical light, and were remade periodically depending on the occasion. They can create ice on walls, and so could announce their presence. They could create artwork of light in the ice.