Riley, I was a manager of this site for some time and there are a few things for which one could be banned immediately, such as those, who come into DCS to do nothing but SPAM. Occasionally, a member, who has been here a while, and has contributed things other than SPAM, will post a link that could be considered to be SPAM. I know and I'm fairly certain that all the current managers do look to see before they ban someone for SPAM to make sure that it really is just a SPAMMer, generally a bot, and not a member who just happened to post a link that is in violation of the SPAM policy.
However, getting banned for misconduct is taken much more seriously and is only done after an individual has shown a consistent pattern of misbehavior and, even then, only after there have been warnings. I assure you that the last thing that the managers want to do is to ban anyone, and, while those, who really don't know why someone may have been banned, might disagree with me, in all the cases that I know of, the person, being banned, really was not so much banned by the management as by their own continuation of the actions for which they'd already been warned about.
You ask if someone can change their email address and bypass the ban. The answer is yes. Someone suggested that the ban be done by IP but even that isn't foolproof because, unless you happen to have a permanent IP address, and very few people do, even that can be bypassed either because the IP address got changed when it came time to renew it, the person disconnected themselves or got disconnected from their ISP's server and had to reauthenticate, usually resulting in a different IP address, or they logged on from a different location and thus a totally different IP address.
I'm also fairly certain that there are at least some people, who sneak into DCS again after being banned. However, since most people can easily be identified by their style of writing, if they do, unless they want to be quickly banned again, they keep a very low profile which is generally what management wanted them to do in the first place.
Also, the decision to ban someone from DCS is never made by just one manager. A consensus is required and, while the number of people banned for such misconduct, can be counted without using all the fingers on one hand, a more common complaint is that management here allows certain people to stay around whom they think should be banned.
Also, when someone does get banned, the management will not answer questions on why it happened. The reason for that is that they respect that person's privacy and, while that often means taking a lot of heat from people who don't understand or know why it happened, I think that it's a very good practice. The only exception to that is, when the person themself, chooses to make it a public issue on this site, and even then, management generally won't go into specific details.
Now, the most recent post about banning had to do with being banned from chat, which is not a permanent ban. At one time the maximum ban time was 24 hours. Now, as I understand it, the time is 15 minutes. So, being banned from chat is not a permanent ban. Because of that, and because the need to stop someone from disrupting chat is usually fairly immediate, an individual manager can and sometimes does ban someone without consultation, although, even then, if possible, and if there is more than one manager present, ban or kick a person or in some cases, persons in order to allow them to cool off and stop the disruption in the chat room.
I'm not a manager of DCS now, but that is how things were done in the past, and as far as I can see, those policies and practices continue to be in force.