To answer your last question first, yes these watches have gotten lighter and are much better. The one thing to keep in mind about the size is that the 45 has a rounded watch face so if it is too small or too big it will look strange. My wrist are 7.5 inches around and the 45mm was just about right.

As for construction quality, IMO it has gotten a lot better. My Vivoactive HR had several issues with band and display. The newer watches are well made and their bands can be easily replaced if they were to break. The display quality seems to be better too. I haven't had any issues with them. Plus the displays have a bezel so it's easy to install a screen protector to prevent scratches.