Magnus did nothing wrong? "lol.", said the Emperor, "LMAO, even."

I finished listening to "A Thousand Sons" a week or two ago and I've been giving it lots of thought. There is the common ironic meme amongst the w40k fanbase of "Magnus Did Nothing Wrong" when he flew face first into the Emperor's webway project and irreparably destroyed the wards and seals protecting Terra from the warp. Think, y'know, a ship without gellar fields except it's a portal between realspace and the warp. After Magnus' breach (which was indeed made with the intention of warning Big E about Horus' betrayal), the Emperor reacted... poorly, to say the least.

If there is one criticism to give the Emperor is that he overreacted by sending the Space Wolves to burn Magnus' homeworld, Prospero, to the ground and fight their way through their fellow Astartes to capture Magnus. Surely a "son, i'm disappoint" and the sternest of stern talkings to would've sufficed. But on the other hand, Magnus became the single reason that the Emperor had to focus so much of his energy on keeping the webway breach shut using his psychic power. Power which could've been used to whoop Horus' ass even HARDER than he already canonically did.

Part of me thinks that the webway breach was indeed the first nail in the coffin for the Imperium that Big E envisioned. It only got much worse from there.