From my experience 3dsMax performance drops significantly whenever the viewport contains hundreds of instances of any object type, not necessarily lights. Everything is fine if these were all attached to one object, (or scattered i.e with ChaosScatter instead of being manually instanced) so it's not about a polycount, but rather number of objects instanced in the viewport.
Can you test if in your scene, same scenario with instanced boxes instead of lights, would give you the same fps drop?