Frankly, Trent leaving smacks of tapping up - which I suspect was the actual reason for a nominal transfer fee. And whilst I don't particularly agree with booing ex players, I believe Alexander-Arnold made the wrong decision to leave. Similarly to how I believe Zaha made the wrong decision. However, you can't fully blame someone for preferring to live in Madrid than Liverpool really.
But, genuinely, he could have won more with Liverpool and played against a wide variety of competitive teams. Real Madrid will be like Celtic and Rangers in general in their domestic league and cup - there's little denying that.