With an extra forum member, clearly, that would be wrong.
On the other hand, somebody pointing out "hey, don't play two supernovae in the same turn" or "entropy's used a lot of grabbows" or "nightmare counters fractal, you dummy," or "you forgot to make a mono" while looking over your shoulder isn't significant. I think it'd be hard to write a reasonable rule barring general common knowledge, especially with regards to regulating people who aren't even part of our community. Otherwise, I welcome the day when we say something along the lines of "thou must command thy Elements in secrete by yonder darke wood neath the silent embrace of blessed Lunaris upon the sixth bell."
I agree with your last paragraph. However, it does seem that there is more than just the examples you gave. To me, these are the important lines:
[2016-09-25 14:47:59] serprex: She even builds some of the decks
[2016-09-25 14:48:04] serprex: Like the air domin vs Water last round
[2016-09-25 15:03:12] serprex: Kae was given vault info, how else could she build decks?
[2016-09-25 15:31:54] serprex: I restricted access to only members + wms + kae
And then from the rules: 'A player caught telling team secrets to anyone outside their own team will face consequences decided on a case-by-case basis'
To me, I think the argument should be how much of a competitive advantage was gained, not whether there was one - by these four quotes, Light appears to have an extra person effectively acting like an extra team member, in that they are building decks and actively given exclusive vault access. Even if WMs decide the appropriate punishment is zero, I think an investigation would be appreciated by many as in the best interests of the spirit of war.
Would you be comfortable that this, without a doubt, is 100% acceptable in the context of War, in your own team?
Would you permit it if you caught wind that this was occuring in your team?
This would not have been permitted on any team I was General of, and no General I was playing under allowing such would continue to have my support.