You are comparing borders that have mostly had the chance to settle into consenting national identities over the past two thousand years to borders that were forcibly drawn in the late 19th/early 20th centuries (in some places disrupting existing nationalisation processes), as if Europe did not also go through periods of unrest and instability in the wake of dissolving empires.
That is besides the fact that (for example) there are far more extant ethnic groups in my country alone than in all of [Western, if not the entirety of] Europe - the considerations when it comes to building a nation are simply not the same. There's nothing that irks me more in these discussions than "Why haven't you already done what took us centuries to do naturally in the space of a few decades under artificial tension?"
That is besides the fact that (for example) there are far more extant ethnic groups in my country alone than in all of [Western, if not the entirety of] Europe - the considerations when it comes to building a nation are simply not the same. There's nothing that irks me more in these discussions than "Why haven't you already done what took us centuries to do naturally in the space of a few decades under artificial tension?"