For in-element battles, the ban-list will be established ahead of time, so we can prepare the decks we want to use and double+triple check them to make sure they are legal - the rules are not too simple, but managable, so I can go in with a planned order of 5 decks that follow the graph-rules.
However, for off-element battles (which is the majority for me: 3 out of 4), the banned cards are decided right before the match via chat-PM. This means, that we are practically forced to speed-build the decks, which could easily lead to illegal decks.
The only other alternative is to build a large number of 5-deck chains and then based on what 3 cards the opponent bans, drop the ones that use any of those cards and pick from the rest.
I would prefer to be prepared rather than speed-build, but I'm not sure I can prepare enough decks to guarantee that a chain-of-5 will always survive the ban-list no matter what my opponent picks.
So, what I'm trying to suggest is to settle the ban-list for off-element battles ahead of time via forum-PMs, rather than doing it on-the-spot when we meet for battle as that would lead to speed-building and illegal decks.