You're both completely wrong. This is the narrative the five eyes and three letters need you to believe.

More important and more funded than domestic spying, US intelligence exists to facilitate regime change. The objective is to have both dragnet and targeted surveillance to obtain leverage (for strategic leverage, blackmail, or comms interception) over foreign political, social, and business leaders so they can maximize the unequal exchange between the US & developing countries.

Keeping Africa, South America, the Middle East, and South East Asia from developing through political and social instability not only prevents them from competing with US exports, but more importantly keeps their economies dependent on natural resource exports, which they need to sell for cheap because they are dependent on technology imports.

China as a manufacturing powerhouse threatens these unequal trade arrangements by supplying these undeveloped or developing countries with manufactured goods and technology, and thus is one of the primary targets of US covert regime change operations. (Also why you see news media crying bloody murder about China's "dept trap diplomacy"). Much of this also applies to other developing powers that resist being imperialized or oppose US geopolitical goals like the USSR/Russia and Iran.

So purpose #1 of the great firewall is to prevent the US from controlling its social and technology sphere and using it to cause instability.

Purpose #2 is economic protectionism for China's high tech sector. China knows that as long as it remains primarily industrial / low tech manufacturer, it will always be threatened by US intervention.

By moving to high tech, China can eliminate its reliance on Western technology imports, eliminate threat vectors for adversaries to slip in, and let other rising nations like Vietnam, Brazil, Malaysia, and Mexico take some of the heat off them by outsourcing its manufacturing there. China also gets to benefit by having cutting edge tech that will benefit its public health, increase education levels, strengthen its military, and form the basis of its post-industrial economy.

China "enforcing the official narrative" insofar as controlling public opinion is of far lower importance than denying the west avenues to destroy its society. China is incredibly diverse and a quick peek into Chinese social media reveals no shortage of western culture fetishizers, religious quacks, conspiracy theorists, anti-vaxxers, capitalist enthusiasts, shit talkers about political figures, and people pushing back on "the official narrative". VPN usage is widespread. People read, share, and meme western news and social media.

Yes they censor posts, no they don't do that great of a job at it...because the goal isn't censorship, its about denying the West the ability to exploit discontent to destabilize the country.

See also:

• Tibet in the 50s & 60s (notice the gap here, when the US thought China would be a useful bludgeon against the Soviet Union & allies)
• Student protests in 1989
• Honk Kong in 2019
• Xinjiang when the US was in Afghanistan
• Taiwan tensions and weapons sales ramping up now

All of these being natural internal tensions exploited with great effort and to great effect by the US through mass media campaigns, radicalizing extremist and separatist groups, weapons transfers, and direct involvement in helping people commit violence.

And the US isn't Russia buying $10 million worth of Facebook ads and running not farms, this is the most developed, most funded, and most sophisticated intelligence apparatus in history. One so large, people with an interest in politics and spying, cannot name all the publicly known agencies without missing 5-10.

You can quote me on this, if the US were to fall in the coming decades, the firewall would also fall within the year. Though, I suspect the US will just languish with internal infighting once the petrodollar loses reserve currency status and China takes the firewall down around 2035 once there aren't powers posing a credible threat to its security.