It helps to understand the context at the time.

The small block faction, of which Adam was absolutely one of the ring leaders, were willing to do literally anything to win. They were and still are collectivist totalitarians. Above it was described as a debate, but it wasn't, it was more like a war. Amongst other things, the small block faction:

• Launched botnet attacks on any node or company that expressed support for big blocks. They took Coinbase offline, they took any mining pool offline for merely allowing users to vote for big blocks. They took out entire datacenters because it hosted a single node expressing support for bigger blocks in its version handshake. One of these attacks was big enough to take out the internet for an entire rural ISP.

• Constantly lied about everyone who was working on bigger blocks. I've actually met people who said they didn't trust me because I worked for British intelligence. I've never worked for British intelligence!

• They wrote a tool to fuck with the vote we were trying to run. Back was fully in support of such tactics: https://www.reddit.com/r/Bitcoin/comments/3hb63g/bip_suggest...

• They constantly manipulated people, promising them they'd work on a compromise solution whilst actually refusing to do so and organizing conferences with rules like "nobody is allowed to discuss solutions to the problem" or "nobody is allowed to make written notes".

... and more. I don't recall Adam expressing any opposition to these acts or trying to stop them. Frequently he was directly engaged in them (not sure who was behind the DDoS attacks, but none of the Blockstreamers publicly asked them to stop).

Satoshi's account had been hacked at that time, and one of the main arguments for raising the block size was simply that it wasn't controversial at all - it was in fact the planned roadmap for Bitcoin from day one, that everyone had signed up to and that Satoshi had discussed. Given their willingness to lie to everyone else and use outright illegal tactics to win, would a small blocker have forged an email from Satoshi? Absolutely they would, which is why nobody cared about it and it made no difference. Especially as that email inexplicably refuted a position Satoshi had repeatedly defended for years, without explanation.