No. Operations like removing blocked user comments, tracking your subscriptions themselves (showing only yours when you're on teh subscription tab), and tracking your sessions are all database heavy operations. You would be trading database heavy operations with "origin needs to send activity pub messages" to you. Activitypub messages were already being generated and is simply just also sent to you... it's very little network traffic and that's it.

As long as your instance views most content it receives at least once... you're well above par for doing your work to lighten the load on the origin server.

As I understand it, there are two kinds of costs that need to be considered: the cost of viewing content, and the cost of receiving content. The first is incurred every time you access your instance and is limited to your instance, whereas the latter is incurred every time something you've subscribed to has received an update, and is incurred not only by your instance but also by the server hosting the community. My concern is that, while hosting my own instance would reduce the load on other servers by absorbing the first kind of cost, it would also increase the load on other servers by increasing the second kind of cost.