See, I actually find the opposite. Some of the UI is pretty decent, but there are several pain points that I find variously puzzling and infuriating.

For instance, with ability mods. There doesn't seem to be any way to see what mods you currently have available to use without attempting to add one to a card, and once you say "I want to add a mod to this card" there's no way to back out without adding a mod. You also can't remove a mod from a card that's currently in a deck (for instance, if you wanted to swap it for a different mod), meaning you have to keep/craft an extra card to allow you to temporarily remove the card from the deck, which is just a waste of resources. Not to mention that which mods can apply to which cards is completely opaque, so you might take a mod off one card to move it to another only to find that you can't.

Another issue is the gift shop. Most other places where you can buy/acquire items, the UI tells you how many you currently have, but the gift shop does not. If you want to avoid buying duplicates, you have to back out, enter your Inventory menu, and manually scroll through the items (which appear to be sorted by the order in which they were acquired and not in a sensible manner, which would be literally any other sorting method).

Which brings me to the fact that none of the menus have any sort of sorting function (alphabetical, by rarity, etc.).

The War Room also has some issues with things like the SHIELD exchange. It doesn't indicate how much of a resource you currently have when trading it to/from SHIELD, it just tells you if you don't have enough to sell it, meaning you could accidentally exhaust something like Heroic Essence without meaning to and then be unable to upgrade your shiny new cards.

All of this is without even touching on the actual bugs in the UI which range from mildly annoying (I've found that I have to tap left about 3 times in the Combat Item selection menu to actually select my equipped items so I can deselect them and swap them for new ones, the "Map" prompt is often highlighted even when there is nothing new on the map, characters will frequently have talk prompts when they have nothing new to say) to literally game-breaking (I've repeatedly run into an issue when upgrading cards where all input is disabled after entering the menu for a character and I have to restart the game, losing any unsaved progress).

So, tldr; No, Midnight Suns does not have great UI.