The rule is fair. When you are capable of doing a 3Axel, it's silly that you HAVE to still do a 2Axel in your SP after completing a 3Axel+2Toe combo.
It wasn't instituted at a time that makes it fair to the
field. The ISU didn't allow the men to do a solo 3A or a solo quad in the SP until
many had proven over the years that they were capable of doing the jump. They didn't institute the rule when only
one male skater was capable of doing a 3A or a quad--because that would have given that skater too big of a competitive advantage in the short program.
Same for the ladies with the triple out of footwork, or the triple/triple in the SP. They weren't allowed to do it until numerous ladies had shown they could do it over a number of years; it was proven that no single individual would be the sole beneficiary.
It may have been silly that Kristi Yamaguchi and Midori Ito were doing doubles out of footwork in the SP in 1992, and you can say that the ISU was overly cautious, but at least they never gave one skater a big leg up over the others in the short program. Until 2010, that is.
3Axel+2Toe is more difficult than 3Lutz+3Toe, yet it's worth less points under the current CoP. Think about it.
This is really a separate issue. I wouldn't have a problem with a combination bonus that awards bonuses based on the difficulty of the first jump (and if necessary a smaller bonus based on the second jump).
But why automatically blame the system as opposed to the skater's strategy? Mao's decision to attempt the 3A/2T instead of her 3F/3Lo (which is ALSO worth more than a 3Lz/3T AND a 3A/2T) was questionable. Had she stuck with the 3/3, she probably would've gotten it ratified at the Olympics.
There is definitely a weakness of the system that doesn't explicitly reward combinations, but it applies to numerous skaters and situations, and Mao was not being singled out. When Yu-Na switched her SP layout from 3F/3T and a 3Lz to a 3Lz/3T and a 3F, she gained nothing in base value though the difficulty of her combination increased. A 3Lz/3Lo, which Miki was attempting, was worth more than either a 3Lz/3T or a 3A/2T, but did anyone complain about that? No.