You can use Rhino 5 like Rhino 4, if you do not enable Annotation scale for text, dimensions, and hatch on the setting page in Options -> Annotation.
Optiion A - Legacy Style: Make sure to set the model dimension scale in the dimstyle now in Rhino 5. There is no global dimscale, it is now set in each dimension style. And set the dimension text height to the 1:1 plotted height, like 5 mm, for example. Then if the layout detail scale is set to 1 layout unit - 10 model units, and the model scale in the dimension style is set to 10, 10/10 will bring the text height back to the desired 5mm, for example.
Of course, option B would be to enable Annotations scale, in the Dimstyle set the values of text, arrows to plotted size like 5mm, (Set the model scale so dimensions are read-able in Model viewports.) Also edit Text heights to 1:1 like 5mm high, set hatch scales to 1, and you should be all set to use the new annotation scale.
It would be best to get your model. If you want to send me a your Rhino model, I will set it up for you. Please email Mary@mcneel.com. I would be happy get your model configured to use the Rhino 5 annotation feature or the legacy Rhino 4 scaling.
Mary Ann Fugier
McNeel Technical Support