The cold winter is definitely a factor but I'd suspect you have some other issues going on as well. The euonymus may very well have scale - an extremely common pest - and the black spotting may be the evidence of that or the development of sooty mold on the scale excrement. You will need to examine these plants carefully or post photos here of stems and foliage. Unfortunately, the best method of controlling euonymus scale is the removal of these plants and replacement with a better choice. Many broadleaf evergreen shrubs will develop foliar damage after a harsh winter. Wait until new growth becomes evident and prune back the most damaged portions.

Watering sounds about right. The ride home-something I forgot to ask you about, could have caused the rapid drying down of the foliage. Don't bother with any "root stimulators" or any other gizmos or potions. The plant already knows how to regenerate a root system. All it needs is time. While some others here have immediately dismissed this as "normal fall leaf drop", it is obviously not so, having happened more or less over night. But the combo of the season and the ride home in the wind could account for it. finally, look at the ends of the twigs for buds. If the buds are present and hard and full of sap, not dried out and shriveled, the tree will most likely be fine next year. +oM

You need to have control over how much water your plant gets, AND how much water your soil retains. If a week after you water the soil is still demonstrably wet, your soil is water-retentive to the degree you're sacrificing a LOT of potential health/growth. Ideally, you should be able to water to beyond the point of saturation, so you're flushing the soil of accumulating salts as you water, without the need to worry the soil will remain soggy so long it limits root function or wrecks root health. Using a 'tell' can help you avoid watering before it's appropriate, but it can't fix that period of soil saturation that causes limited root function and poor root health. There are ways though, to limit the amount of excess water a container planting can hold. If you have interest, This Should Help. You might also find this Basic Overview to be helpful. It should help you avoid all the most common pitfalls hobby growers encounter early on in their growing adventures. Al

you dont mention size .... is it small enough to shade it???? there is no doubt in my mind.. that transplant shock is a big part of the equation ... see link about timing https://sites.google.com/site/tnarboretum/Home/planting-a-tree-or-shrub as to water.. take a hand trowel.. or tablespoon .. and dig 3 to 5 holes 3 to 6 inches deep ... around the tree.. in the undisturbed soil.. and gob planted.. and the fill soil ... and FIND OUT about moisture in the soil ... and then water accordingly ... in good draining soil... properly mulched ... i would be surprised if it needs water more than once a week.. a good deep drink ... with full drainage ... subject to heat.. rain.. etc ... how it all works in your yard.. in your area.. is mostly left to you and your trowel ... whether or not a tree can deal with excess water .. a transplant is a different beast ... and stressing it more.. by moving it again .... is not an option.. imo .... btw.. how is the mag doing.. that you moved??? ken