Not really, don't forget that Agent has Persona which means Overwatch. If my players would be stupid enough to implement something as ridiculous I would make GOD run into them after 2 minutes "oups, your agent has try to hack a DR7 commlink and utterly failed, and it has rack up his OS score..".
Also, bear in mind, that Agent are allowed to perform "one matrix action" on behalf of the user. So, even if it seems logical for anybody knowing anything about (actual) software, it is possible to program an Agent to say: "Matrix Perception on Device, if DR < X, then Hack, Hack, Steal and Reboot".
So, IMHO, making Decker or Technomancer irrelevant by a smart use of agents is more of a rooky / bad GM issue than anything else. Obviosly a skilled (meta)human being or an IA, can be far more efficient.
Actually I did not intend that as a way to replace a Decker, especially because, as a GM, I consider Agent to be as dumb as Drone, so they can't really do anything smart unless someone instruct them. And I would not allow a non-decker character asking his agent to "hack something" for him/her.
(well, unless, this is how the group has decided to the lack of decker. But I would still strongly limit this use case).
No, the intend here was to provide a new/interesting opponent for my decker player. As a GM I don't think I would allow such build to a player,but when it comes to the matrix, don't forget that the Megas always cheats
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