That is the problem with people at the moment. If the USA has it we must have it, if the USA has this much we must have this much. USA isn't the benchmark for everything. China's military is built around necessity, it puts economy first above everything else and the military grows accordingly to defend that economy. Military strength should be based on the size of the economy otherwise you end up where the Soviet Union, USA and Australia are at.
China current fighter inventory quantity is sufficient. The just need to phase out the 3rd Generation fighters. Evidently we see a trend where J-8 are replaced with Flankers, J-7 with J-10 and Q-5 with JH-7A. Now JH-7A numbers already surpass your low figure of 150, we are in the ~220 mark for JH-7A. It seems from observation that the production of JH-7A has been moving very slowly, possible indication of a new variant of JH-7 or something else entirely new. J-10's production have been slowed down, we have seen the J-10B been in testing for awhile now. High and mostly probable indication that the J-10A production line will cease were the J-10B will replace it.
I don't see the need for PLAAF to acquire 300 J-20. Mid 100's should be sufficient in protecting China's airspace even against the most strongest airforce. The biggest problem for PLAAF now is replacing the large number of J-7, and also engines now they can make small batches with good quality. But the problem is they cannot make enough to meet demand of what the PLAAF needs. They got to power J-11 & J-10.
My thinking is certainly not on the lines of whatever America has, China should have, rather, in terms of what China ought to have, being the second largest economy in the world and a superpower. As such, it is very important for China to protect it's economic interests.
Have seen the latest Oil Prices lately? Did you know that China had invested $18 billion in infrastructure development in Libya's Oil Fields? Did you that the new Libyan government is giving strong indications of not taking up those projects with China anymore, reasoning that China didn't get involved in the NATO military campaign against Qaddafi?
Isn't that an economic loss of massive proportions?
Also, take Sudan as another example, how much did China invest in that country? $20 billion in development and infrastructure like Dams, Hydro-Electric Power Stations and Textile Mills. Did you know that Sudan was one of the largest exporters in Africa of Oil to China? Did you also know that the Dafur area (which became independent of Sudan) is where majority of the Oil Reserves are located? Also, did you know that the new South Sudanese/Dafur government is not really willing to do business with China?
Both of these are prime examples why China, as a superpower, owes it to itself, the need to expand its sphere of influence. Of course, the only way that is possible, whereby China expands it's military and establishes bases in the countries where it has investments in. And also, when there is a power vacuum in a country, then there is every chance that the West will meddle internally to destabilize the peace in the country.
This is what is happening in Syria as well, where it is Russia who would get hurt, in the event that Assad's regime gets toppled. Russia is banking on Assad's survival, since the only overseas military base that Russia has, is in Tartous, Syria. Russia invested in upgrading the base and building it from the ground up. The reason for this, was because of the deteriorating relationship with Ukraine, where Russia's lease on the Crimean Naval Base, is about to expire.
Today, we see Russia scrambling to send military hardware to Syria, in a bid to see Assad crush the Western sponsored, terrorist rebellion in Syria! However, Russia doesn't have the military capacity to openly challenge the West on foreign soil. As this isn't the 1970s and we're no longer in Vietnam. A militarily weak Russia, offers little challenge to the West that is consistently running Black-Ops in countries like Libya, Sudan, Syria and Pakistan.
Everyone says, convincingly, that it is because of Oil. But that is not true, rather it is because the collective Western Power Base, doesn't want to see China or Russia rise to power, economically or militarily.
Hope you understand what I am trying to point out. And if you do and still disagree, I am anxious to know what your strategy would be, to counter the increasingly arrogant West.