Mobile also happening like the same.
Main problem is not showing the attack boost purposefully in mobile and cannot hover in mobile (kind of handicapped).
Thinking like, it should be added as an idea to get the improvement. It doesn't affects anything on the game point of view.
But, design wise it has few trouble as per my guessing.
Tooltip displaying the information is one time adding on the development design work. It won't get changed dynamically as a design thumb rule until that item or object completely replaced. Honestly thinking like, to implement the coins rush behavior they avoided tooltip UI and brought window UI design mechanism to handle the timer values. It's purely development use-case on design perspective.
INNO/FOE devs can take this as a change request or development miss for mobile and display the attack boost value next to age label with swords icon in the same window. Simple change.
Like below image,