I'd say the opposite, intra-EU trade is more like international trade, at least for B2C. Each country has its own national market situation, companies cannot easily expand to the entire EU because in every EU country they will find different local competitors who know the local market much better than they do. Every product has to be localised for the local language and culture. All marketing has to be localised.

Despite efforts to the contrary the EU functions as a glorified free trade zone, half a century of integration cannot beat 1000 years of fragmentation.

Just to be clear my statement has nothing to do the 'EU' which is largely a trade body. I specifically used the term 'Europe' and 'free markets' not 'free trade'. This has nothing to do with Brexit to avoid confusion.

Not true at all - EU does make things simpler but it's still very different legal systems, currencies and even languages.

Why? What's the difference between USA-Mexico trade in car parts and intra-EU trade in car parts?