It is certainly true that international trade agreements impose various contractual obligations. I am sticking my neck out a little on this one, but I think only the EU insists upon its own, highly activist supreme Court, can act as arbitrator in disputes. In most Treaties dispute arbitration bodies would be expected to be independent and neutral.
This legal imperialism, by which the EU always seeks to impose its own legal regulatory order onto countries both within and without its membership, is central to its current disputes both with the UK and Switzerland.
Having to deal with laws and courts and things like that, I can answer this one. International trade agreements between countries are usually arbitrated under a mutually agreed arbitration court, often in a neutral country. However, the EU has an overarching law framework, and, in order for this to work, there must be a court that can decide on matters relating to that law, hence the CJEU. If you don't have this overall framework, you hit problems.
For example, in my world, infringement of a European Patent granted by the EPO (not an EU organisation - e.g. Switzerland, Norway and Turkey are contracting states) is heard under national law. This can lead to some very odd results. In one case, the UK High Court and the German Bundespatentgericht came to exactly opposite conclusions on the same set of facts (German patent law has a rather different concept of what the skilled person would know). This is the reason for the interest in a Unified Patent Court covering the EU. The German Bundesverfassungsgericht (Federal Constitutional Court) has recently thrown out attempts to block German ratification, so it looks as if the dream of a Europe-wide patent under the auspices of a single court will proceed.
So, given the nature of the EU, it was inevitable that a unified legal framework would, indeed had to, arise. You could argue that there should never have been the unified law in the first place and that it all should have been a series of bilateral or multilateral agreements with an agreed arbitration court for each individual case. But this never happened and, for better or worse, we got Maastrict instead.
I see a lot of CJEU decisions in the IP field, and I can see no grounds for thinking that it is other than independent and neutral. And it is certainly nothing like as extraterritorial as the USA when it comes to extending the law beyond its borders.
