You gotta understand memory intensive app such as some photo editing or games will need more RAMs that the system will need to reallocate memory to priority on screen app.
For example, if you run a Geekbench CPU test, most of the apps in background when bringing them to foreground most of those apps will need a refresh.
And taken into consideration, apps do get frequent updates with more added features that may require additional memory to run. iOS can be improved for better RAM management but it may also be hardware limitation 2-3GB RAM on certain devices that’s a reason why Samsung S9 has 6GB RAM.
While true take a look at my entry (#70). For my experience it isn’t the memory intensive - that I would expect. 10.3.3, while not perfect, was better than 11.x. I am unsure of what Apple changed, but change it they did. Tasks I used to perform on my IPP I now do on my PC or MB as I cannot count on the IPP to consistently execute them.