You are both right in a sense. Economic interference caused a huge downturn to the production of steel in the U.S. and the 70s and 80s, and outside of putting in some agreements for quotas, (Carter and Reagan IIRC) not much was done. U.S. steel rebounded some, but it is still down something like 300,000 workers compared to the 70s, and the effects completely ruined a few cities. Much of this came from other countries producing steel more efficiently (just like the U.S. helped Toyota, we helped Nippon). So foreign steel, not burdened with outdated equipment and process, were able to undercut us, not to mention foreign subsidies that undercut the world market. It is exactly what China is doing.
Obviously it would be better to have no interference. But we've been dealing with other countries that are very good at manipulating the market.
So yes, the U.S. produces a very small % of total world steel. Part of that is due to interference from other countries. Part of that is our own fault.
So I don't see this as something that will allow us to start exporting steel. It is designed to bring some parity to the steel market without punishing those countries that aren't manipulating the market (the proposal will allow countries exemptions if they can show their steel practices are manipulating the market. There are already exemptions for CA and MX, and there will likely be one for JP and the EU.
Regardless, I do see this as raising prices for consumers.