The claim of iOS using up too much of the iPhone's memory is bogus. . . especially compared with the competition even if their is a class action lawsuit filed. As a factual matter, iOS is much more parsimonious of memory than is the completion. Look at this graphic to see the usage of comparable flagship smartphone's and the amount of available user memory after the installation of their OS is installed on a basic 16GB phone:
Memory occupied by the OS in that figure is a static measure and, moreover, is not necessarily a measure or predictor of performance vis-a-vis CPU, graphics, etc.
Ther can be no doubt that iOS 7 and especially 8 place an additional burden on existing hardware resulted in degraded performance, response, etc.
A separate issue are the changes in functionality trumpeted as improvements but in far too many cases the changes are arbitrary, unnecessary and/or unwelcome. But standing pat doesn’t sell phones or apps so the process is forced.