Its indicative of Leviathan's ability to still use technology, and if it is a remnant it shows their technology can last in working order for a billion years. Surely it would not be the only technology to do that.
What is your argument for the Leviathan having "very little"?
I believe earlier that you said they would not have technology, or at least very little, to avoid Reaper detection; however the Prothean base at Ilos shows they just needed to be off the grid (not in any databases) to avoid detection.
I'd imagine that a billion years of enthralling other species with said orbs to maintain (and repair or possibly disseminate what ones remain) might have something to do with that. You keep up regular upkeep to a car, or a lamp, or a PC, or any tech, you can make it last indefinitely. Otherwise, it's complete speculation based on nothing beyond said speculation.
My argument is that there is absolutely no other form of technology seen to be of Leviathan origin beyond the Catalyst, the Citadel, and the Reapers themselves. And they really aren't being used for the benefit of the Leviathans. So beyond the orbs (hence the 'very little'), we see no other forms of Leviathan technology being used by them, and, unless shown evidence otherwise, I remain skeptical of your claim.
I said it was a possibility. I never stated it as truth, but I will argue in defense of it; The Reapers are based off of Leviathan technology. As the game shows us, the Reapers are actively tracking Leviathan technology, because they correctly estimate that the Leviathans would be a grave threat to them. I postulate that the Reapers are specifically looking for and tracking Leviathan technology. That is why the Leviathans might have so little tech or none at all. The Reapers know what to look for, and they know how it works, because they themselves are based off the technology.