Lowe Flieger,
Not a simple question to answer. There are disadvantages and advantages to both The West, and to Russia in their solutions.
1/ Cheaper aircraft mean you can afford to purchase more of them. More of anything is generally a good thing.
2/ The more complex an aircraft the more expensive it is and often it is less reliable than simple aircraft.
3/ The older an aircraft model, e,g. the Tornado, the better it is in some ways. All the kinks have been worked out of it and it now works as it should have done all along. Unfortunately the design is now out of date and there are more modern aircraft on the market
4/ The more expensive an aircraft, the better it should be at picking up an opponent, avoiding detection. The more likely it is to achieve its aim initially. The problem is, if it makes it back home it is liable to require more maintenance than a simpler aircraft prior to being able to fly again.
5/ Complexity can be overwhelmed by numbers. There is no point having 100 hugely fantastic aircraft with a kill ratio of 1 to 10, when the opponent have 10,000 aircraft.
6/ An overly complex aircraft reliant upon computers to fly will not be very good when the computers that help fly the aircraft go wrong.
7/ An overly complex aircraft may kill every opponent it sees, with a capability of shooting down 144 aircraft at the same time, but if it only carries two missiles, all that technology is not much help.
8/ Spending huge amounts of money making an aircraft hard to see electronically can be extremely problematic when the opponent spend relatively little money finding another frequency that the aircraft can be picked up on. Whoops! You suddenly have an aircraft that is easy to see, which has design limitations on how well it flies, as it has compromises on how well it flies due to being hard to see (originally).
Designing an aircraft is very much a case of compromises; what compromises are you willing to accept to meet your requirements?