Well it’s not 100%, but it is about 95% without Russia Restricted and probably about 80% with RR.
Everyone is skeptical about it at first and rightfully so - if two relatively inexperienced players are playing each other, the game is pretty balanced. But ‘certain Allied victory’ is an important concept that signifies the transition to advanced player, and from then on you will always play with rules that bolster the Axis. Here is the catch: the game is only unbalanced when the Allied player is experienced, and only when they use one specific strategy. Many players criticize Axis and Allies by saying that once you really learn how to play, it is the same game every time. This is mostly true for the early part of the game, say the first 5-8 turns or so, but advanced players find enjoyment in the more subtle aspects of the middle and end game.
There are several websites and posts in this forum with the the specifics of that strategy, but here are the basics:
1.) All 3 Allied countries concentrate on Germany and ignore Japan as much as possible. The goal is to defeat Germany before Japan defeats Russia. This is done by playing conservative and buying large amounts of infantry every turn. Time is on the Allies side.
2.) The UK and US build protected transport fleets that shuttle large amounts of infantry to Norway every turn. This infantry then travels to Karelia and puts overwhelming pressure on EE. Also, some can head east into Russia to help them defend Japan if needed.
3.) The Allies agressively kick Germany out of Africa so that Germany doesn’t have extra income to help defend themselves in Europe.
#2 is the key. Picture 5 US transports and 4 UK transports in the North Sea dropping off 18 Allied infantry into Norway every turn and you will get the idea. Karelia will never be in danger of falling, and it is only a matter of time before EE does. Also, this navy threatens WE, Germany proper, and EE every turn. This really forces Germany to spread itself thin. Also, keep in mind that the Allies have a 1-2-3 punch with the UK, US, and Russia all being able to attack the same German country in one turn.
Most A&A games are played with Russia Restricted and bidding for the Axis. You can find posts on bidding in this forum if you are unfamiliar with the process. If you want to simulate the most common bid, give Germany two extra infantry in Libya at the beginning of the game. This prevents #3 above, which in turn helps Germany gain the extra income it needs to defend itself until Japan takes Russia.
Also, it is very difficult to get an Axis economic victory against a good Allied player because they will be very aggresive in Africa - it is easier to take Russia with Japan.