One of the ways you can set the text size in dreamweaver is on the Properties window.
First make sure the properties window is visible then highlight the text you want to format.
In the properties window click on the css button (left side of the panel), here you will find drop downs for setting the font and the size.
By default this will create a new css rule at the top of your page (in code view) you could also use the targeted rule dropdown to change it to an inline style if you preferred.
That insane if the HTML method is totally outdated
you can still underline, strikthrough, bold and set fonts using HTML so why not set font size as well
what happens if you need to set a font size that only applies for one paragraph or 1 word or something. resorting to the CSS area is not a efficent way of doing this?
Dont take this the wrong way but the w3c don't even want you to set the the font using html any more, the other tags they have killed of recently include <center>, <s> and <strike> for strikethrough, <u> for underline. They also don't want you to set text alignment, background color, or text color using html attributes anymore either.