Want a real shock? Look up what it costs to send a 4lb package from the us to China, the exact same package they pay $18 to send.
Also for big mailers, they are even subsidize in US shipping.
This is kind of political theatre, US sellers will never match up with chinese sellers even after this change, even not in 5 years.
US is trying to close this 75M usd gap in 5 years with this agreement, what china will do? They will just subsidize 75M more.
This 75M will not make any difference in US pricing of mail. Chinese will continue with free shipping, US prices at best will get little lower.