You perfectly know that: 1- they could chose to make the explorer private if they wanted to 2 - people don't do tx within the Spark entity and just use it as a LN wallet. I know its still possible to find your spark adress through your LN invoice if you are technical enough. But as soon that they stop reusing address this almost stop being a concern because most of Spark txs are in fact LN swaps. So it breaks all deterministic links for an outsider. But the main flaw come from the fact that they made the explorer public. WoS could have also made their database public before bein on spark. What I mean is that the problem come from a choice from this specific Spark entity not from the protocol itself.