Wellies are fine until your twist your ankle as fall through a bit of rough boggy ground. Then you have a very painful walk home.
It’s why those who do things on rough ground wear really sturdy boots with good foot and ankle support, and more importantly grip and the ability to get the support and grip needed to go up, down and across steep and usually slippery slopes.
And if you are worried about feet getting we, use good winter standard gaiters. Or just accept you might have damp feet, and have a change of dry socks for later in the day. Far far better to have damp feet than twisted or broken ankles, or worse and you take a tumble.
Every year several people die in the Scottish wilds. Usually they lack proper boots and clothing. That quick ramble can easily turn into a life threatening event when you take a fall, the weather turns and before you know it, the car or argocat that is 200 yards away may as well be 1,000 miles away because you have twisted an ankle, are in a lot of pain and its now ****ing with rain, freezing and 40 mph plus winds. And you have no signal in your phone and the battery is dying because of the cold.
So in short wellies and rough ground in Scotland are a bloody silly idea unless you want to feature as a footnote on BBC Scotland local news.