Users use my app and steemconnect as well. When they broadcast the transaction they get the transaction id and block num, then they send it to app endpoints.
Users don't use a third party apps.

If you said it's redundant to use also another protocol and blockchain is the method of communication why do you need SteemSQL then? It is also redundant.

Btw storing the data in the app application makes you independent, you don't need to count on someone's app like SteemSQL (what if they will disable it?)
You do the indexing on your side. I don't see there any disadvantages.

Also you don't need to stream all transactions from the blockchain only those that you really need.