Yes, cliches aren't really good for such a project.
No, the four you mention are not the deadly sins.
There are plenty of wild and popular effects which do no good for the motivation of others.
But you will never catch all of them by writing down a list of them.
Moreover, I didn't miss Hastings or Manzikert. With Hastings, it would have been a mistake to introduce it, as that would have been a contaminant from OTL.
And if we agree and it's plausible, why bother? Battles can often go either way. Completely different populations/cultures (e.g. Vinland) and severe cultural revolutions (e.g. a new religion) are much worse.
How about that:
After a posting, other posters have a certain timeframe (e.g. 24hrs) to utter objections (in a polite and constructive way). And we all should be open to discuss modifications of our contributions. Basically, we should come up with a compromise in the end.
This does not only serve for the avoidance of spoiling wanks or cliches, but also for accidental implausibilities. If there the TL doesn't make sense in 1100, I'm not likely to contribute in 1500.
Of course it takes more time to do it that way, but then we will have done it as a team!

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Second:
The TL here suffered from the specific interests and moods of us.
The result was a TL where a lot happened in the extreme Northwest and Southeast of Europe, and the rest of the word basically sat still ...
This is what we have to avoid. Therefore, we should oblige ourselves to give an overview over all parts of the world including all important entities, on a regular basis - let's say, every 10 years. This needn't come from one player alone, nor necessarily from the latest poster.
But we should put this together before moving on. This reminds all players of other countries than the previous posters have focussed on.
And: We should start with such an overview in 1000 (or whenever you would like to start).
Although I am not completely illiterate in that era, I have to admit I had no idea what your PoD means. Without a accompanying overview, such specialties may choke other people's interest ...