There is a problem with any type of aggregation at current stage. Any relay (even taking the best attempts to collect all the data from all other relays) — will never have a complete picture of events. And thats rather good for the network.

However, aggregation in this case becomes the source of truth that is flawed by default. Of course, it may be used for some estimates but it locks you to the specific relay instance

On the other hand client aggregating all the events from different relay (say, regarding zaps to specific note) is very inefficient and slow but it is able to find “source of truth” on its own