I can't stress enough how much I dislike what Adobe has done to Photoshop! In years gone by, working in Microsoft programs like Word or PowerPoint was an utter garbage experience (and still is to this day) because you spent more time undoing the automatic formatting that Microsoft assumed you wanted than doing the actual work you set out to do. In recent years Photoshop has pretty much become the same experience. It's no wonder more and more people are turning to Canva. What is the point in learning what is supposed to be a "sophisticated" piece of software if you can do the same thing in half the time using simpler tools elsewhere? Everything from moving the location of tools and commands to hidden places (why remove/move 'save for web and devices' from the file menu? just why? It's not that big a deal but why bother? Why give me something else to think about?); to adding in new tools that are used in other CC apps but that now behave in a totally different way to that same tools in other apps (i.e. artboards); to changing shortcut commands that have been in place historically across all CC apps. i.e. holding shift to keep the aspect ratio when resizing. Why change it for JUST photoshop and not Ai or iD or XD? just why? Why did this need to be changed at all? Why is the opacity gauge in a different place in photoshop than it is in Ai or iD? Just why?
Please just stop fiddling with Photoshop. It's becoming un-instinctive and horrible to use. I only use Ps if I absolutely HAVE to now otherwise I'll swerve it as much as possible.
Save For Web is being replaced with Export As. They just kept SFW around until Export is fully finished.
Tools behave in different ways because Photoshop works with pixels; InDesign and Illustrator work with vector data. Two different worlds.
Shift to keep proportions; OK, I'm with you there. But there is a preference to keep the old behavior, just check that and forget it. Supposedly this was done precisely for alignment with other apps, not sure which other apps they had in mind.
Opacity, see point two. You really need to understand that these are very different animals.
Other than that, it's notable that everybody will complain about different things. It's hard to make everybody happy with everything,all the time.