If you do a numeric entry, you first insert one number, then the other.
If you resize using the green and red arrows, simply click in the middle of them then drag to keep the same ratio.

To scale X and Y at the same time using the Scale tool, don't use the handles. Just select the bone you want to scale, then click drag anywhere in the viewport away from the handles (the green and red arrows or shapes).
Spine's primary transform tools (scale, rotate, translate, skew) are designed to be used without needing to hit the handles. But you can use the handles in case you want to perform the transformations in specific ways.

For numeric input, yeah. Currently, you have to enter both.
. 5 tab . 5 enter is enough for that case.

will be nice have universal tool like:

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Haha. I dunno about universal.
It's much easier to use hotkeys than to hit the tiny targets on the Unity rect tool. It's why I think animating in Spine is still more comfortable than in Unity.

I guess if we didn't follow their scheme, there might be a better way.

But corner handles for scale. I can agree that's a good idea.

Justice rains from above.