I hope this doesn't come across as a rant, but as constructive criticism 🙂
First of all, for anyone who doesn't know, a checkbox in the preferences was added in order to bring back the "legacy behaviour".
The point of my criticism is to point out how this behaviour, although is set in the right direction, is very poorly executed. I agree that keeping proportions when rescaling or changing dimensions should be the default behaviour. However, it's not implemented across all tools that utilise such the shift modifier. Here are some examples for current behaviour, whether shift is needed to keep proportions:
- Free transform: NO (new behaviour)
- Crop tool: YES
- Transform selection: YES
- Slice tool select/transform: YES
- Rectangle tool: YES
- Type tool draw/transform: YES
- Needless to say, neither Illustrator nor any of Adobe Suite hasn't implemented this change at all.
In conclusion, all but ONE tool uses the "legacy" behaviour. How is this intuitive for a new user?
To those of us who have used Adobe programs for decades now, it feels Adobe implemented this change in a poorly and lazy manner.
This isn't worrying. However the fact that this stufd makes it through release after release, makes you understand how caotic the development at Adobe must be, resulting in buggy and crash-prone programs.
I can address the "new user" part of your question, because I've been teaching new users for over 30 years. After spending five minutes showing them how to scale images proportionally with the Shift key and all the repercussions of not using it, I would move to the back of the room during the lab and watch at least one person drag the bottom center down, then the right middle handle outward and distort the photo.
For new users, constrain by default is a good thing for photos, especially photos of people. The other things you mentioned aren't photos and do not need to be constrained by default. For example, I have seen Illustrator users accidentally enable constrain for scaling, then wonder why the height of their rectangle changed when they typed in a new width. After trying 5 or 6 or even 10 times, they will eventually call me over to find out why they can't change only the width and keep the height.
What Adobe has done makes sense for new users and is also in line with the way many newer applications work. Experienced users like you and many others can go back to the old way.
In addition to the checkbox you mentioned in Preferences, there is also a Link icon between the W & H text boxes that you see when you use Cmd+T for Free Transform. For me, this is intuitive because the Link button is used throughout InDesign and Illustrator to toggle Constrain for many things such as scaling, margins, bleed, slug, etc.
I'll let others address the parts of your post that are not about new users. 😊