.5 is not a minor update, this is the misunderstanding leading to an incorrect expectation and thus disappointment.
Version numbers of Steinberg software have, for a very long time, followed this pattern:
A.B.C
A - major updates to the software, including changes to UI, audio/midi engine, etc
B - new features and smaller changes to functionality.
C - maintenance/bug fixes resolving any issues with A.B
The business model pricing reflects this release cycle with A and B new feature coming out with very nearly the same timing each year and, if you update continually, A upgrades cost more than B upgrades - and all together ensure Steinberg remains a viable company producing a DAW I like.
Note that Steinberg will release 10.0.C updates in that series whilst 10.5.C is released for a reasonable length of time to get the last of the bugs fixed in the 10.0 feature set. Personally I find this to be a good practice, often lacking in the software industry. It means I can skip a B update if I wish and my older DAW will still be patched for a while longer.
In short, you don’t need to purchase the new B features if you don’t wish to and you will receive C bug fixes for a little while longer at no cost to your existing 10.0.C version. You are in truth receiving what you wanted - patches to your existing purchase for free.