I’d like to start by saying that while I have lived in the UK for some years (in Scotland, Wales, and then England), I also consider myself to be an “outsider” in that I am originally from the United States. Broadly speaking, I’d say that I agree with your perspective about the differences in cultural and historical tensions between Ireland and England compared to those of Scotland and England. The fact most apparently in support of this perspective is that Scotland is still politically unified with England, while (most of) Ireland is not. This is not to discount the long and often violent history of Anglo-Scottish relations, nor is it to say that Scotland does not have a strong national identity or a significant independence movement of its own. However, I think the general idea behind your question is certainly arguable, and there are a few factors that one might posit as possible explanations. Let’s break it down:

Political relationship to England

From about 1600 to the early 20th century, both Scotland and Ireland were politically “attached” (for lack of a better word here) to England, but these were very different kinds of attachments - conquest vs. union of crowns - and came about in different ways which are critical to understanding the relationship of these constituent nations to the eventual United Kingdom of which they were/are a part. In the centuries prior to 1600, England frequently found itself at war with both Scotland and Ireland. The latter, it should be mentioned, was never a unified state, but rather was divided up into various gaelic petty kingdoms and Anglo-Irish lords (I’m simplifying here, but it’s an important distinction to make with late medieval Scotland which was more politically unified, relatively at least). You’ve probably heard of some of these conflicts before, but up to the 16th century, England never had a complete and permanent domination of Scotland or the island of Ireland. The political relationships between the three “nations” in question would begin to change fundamentally during the second half of the Tudor period, from around the mid 16th century to 1603.

To make a long story short, during this time Gaelic Ireland was conquered militarily in a series of wars which eventually brought the entire island under English control as the “Kingdom of Ireland,” the monarch of which always happened to be the same one who sat on the throne of England, fancy that. This process of conquest and remote rule through proxy forms one of the bases for the argument that Ireland was England’s first colony. The way in which Scotland found itself having the same monarch as England was substantially different. In 1603, the “Virgin Queen” Elizabeth died without ever having married, and without a direct male heir. Prior to her death, she named James VI of Scotland as her rightful successor to the English throne (James was the great-great grandson of Henry VII of England). James became James I of England, moved to London, and England and Scotland were united under one crown. The royal house of Scotland had become the royal house of England as well. Scotland retained its own parliament and system of laws, but the political union of the two countries would be completed in 1707 with the Act of Union, which formed the United Kingdom of Great Britain. Note that Ireland is not included in that title of “Great Britain.” It remained a subject nation until nominally elevated by another act of union in 1800, which came with an additional name change to “The United Kingdom of Great Britain and Ireland.” We can see here that the historical processes by which Ireland and Scotland became politically unified with England were fundamentally different in their nature, and arguably Scotland joined the club under much more advantageous and less exploitative circumstances. This is NOT to say, however, that Scotland’s unification with England was (or even is now) uncontroversial or without repeated related violent aftershocks. The ways in which Ireland and Scotland were governed as a part of the United Kingdom differed as well, which sort of leads into another point…