I would think long and hard before adopting this strategy. If the Russian player buys 7 bombers over the first 5 Turns all they are doing is guaranteeing an Axis victory.
No smart Axis player is going to build the Romanian Major Factory. This strategy, known as the Romanian Rush, provides for a greater G6 attack on Moscow. However, it actually provides a weaker G7 attack so most players will not use this strategy.
If you want Russia to be aggressive buying 4 infantry, versus 1 bomber, provides more offensive firepower than 1 bomber does.
A smart German player is not going to split their main attack so having bombers to “pick off a second area” is worthless.
A smart German player is not buying tanks. They are buying infantry + artillery on Turn 1, then lots of mechanized infantry and some tanks the rest of the time.
Having 7 bombers on defense versus 28 infantry is self explanatory as to why that is a bad idea.