what according to your opinion would be the consequences if all yhe blood vessels were of the same size

It depends how big they are.

Explanation:

If they were all the same size the vessels in the legs, then blood pressure wouldn't be high enough for vital organs like the heart.

If they were all the size of the vessels the heart, then it'd be very easy to lose large amounts of blood when cut.

There are probably more complications that I haven't considered, but you get the gist.