Using less characters got you banned? I don't understand why that would happen. I would think using more characters would be more likely to get you banned since it's less like what normal users do.
Well increasing the usage would also increase the number of messages.
How does Whatsapp choose to ban people? Total messages sent? Then increasing the message size doesn't stop you from being banned, it just makes it take longer before you're banned. Messages/second? Then avoiding the ban by a message size restriction seems like a very clumsy way of doing it; it would be much more straightforward to avoid the ban by limiting the messages/second.