Well the price difference between an M4 MacbookPro and Air buys you several docking stations.
Also a MacMini is not mobile, and even if I take the mini, it neither has a screen or keyboard. The thing is I don't need it WHILE I'm traveling, I need my laptop at the destination. And because that is less than 5% of the time I use it, there is no issue in carrying the external 2.5" HDD that I keep on my dock. You personal use-case may vary.
Also a MacMini is not mobile, and even if I take the mini, it neither has a screen or keyboard. The thing is I don't need it WHILE I'm traveling, I need my laptop at the destination. And because that is less than 5% of the time I use it, there is no issue in carrying the external 2.5" HDD that I keep on my dock. You personal use-case may vary.