Are new versions of Premiere Elements as good as old versions for slideshows?

I make videos that mix video clips and stills, including RAWs routinely. 

There are editing controls in Premiere Elements that I use, so I don't know what might have disappeared.  There probably are better tools and controls in Photoshop Elements, Photoshop and Lightroom for stills.

What "precise" controls are you referring to?  I ask because I've never had any issue with using the video editing tools on stills.

You can have all the versions you want installed at the same time.  They operate independently. 

However, there can be trouble opening the same project in multiple versions.   The reason is that different versions have somewhat different tools and features.  If you open a project from one version in another, the project files can be corrupted, depending on what was used.  They might also work fine! 

The solution is to not open projects in different versions, but if you do, work with copies. 

Another caution is that older versions may not fully install.   To conserve space on customers laptops, some themes, music tracks, transitions, etc would be installed from the internet as needed.   As a version ages, Adobe moves on and those older features may be missing and stay missing.  Older versions may also have ties to their original operating systems. 

Good luck and have fun with your projects!

Bill