I guess I just think starting a guide that's title seems to indicate it's teaching you how to play multiplayer by ignoring (his words) one of the largest sources of new players seems very odd. In my opinion, Voobly is the way to step up your online game and get better, but if you want to play casually Steam is by far the easiest to just get it and play a game. In my opinion, focusing on Voobly's positive aspects is a much better way to convince people to move over than attacking the way they currently play. I personally would be pretty upset if I bought the game on Steam, looked for how to play on multiplayer, saw this telling me it was a waste, that I should go use my original disc version instead. If I imagine myself as learning about the game through Steam, overall enjoying it, and wanting to get a little more into the game, reading this document and seeing things like '...no official support for the game...', '..bugged since the beggining but it got worse over time...', '...I will act as like AoE II HD and other fanmade content did not exist..'. I would stop reading, but maybe that's just me. If I play on steam, I know how to play multiplayer, so why would I read an introduction to multiplayer? I do believe Steam players moving to Voobly would benefit from a document like this. Or if Gameranger is really dying (I wouldn't know, it still looked fairly active last time I played), they may likely move to Voobly? Maybe just title it Introduction to Multiplayer on Voobly?
As it is now, it's reads as a guide to get in with the competitive community, and there is nothing indicating how to play casually, or even that this is okay to play casually long term (tons of people have a lot of fun playing multiplayer this way). Many times it mentions pro players and the competitive community. Even the short paragraph about Gameranger, it mentions rankings multiple times and doesn't even mention how to setup, which is my opinion is what I would expect to see in a document about how to play multiplayer. So from reading through it, I have to assume competitive players is the target audience. This is what voobly caters to, but if you're trying to attract casual players, you need to be welcoming to them as well. If I read this as someone who wants to just play for fun 1-2 times a week, I have no idea what I should do/expect (stay in NPL forever? do you move to MS as a 'noob'). It reads like a guide for someone who wants to be competitive. I guess I just don't understand who is expected to read this...
As mentioned before if this is a guide to multiplayer, and not only for competitive players, it should include Steam, Gameranger, etc. I would suggest including a section on LAN play with userpatch (or forwarding ports, etc? honestly not too familiar with this). It doesn't have to be much, but there are some very important differences.