Thanks all for your replies and feedback
In the meantime I have discovered that I am not the first (and probably not the last) user with this question, and that my search magic has failed me to find the following post earlier: I will share it, so that other users may find it:
I have to waste an entire drive just for booting?
I understand and accept the reasoning in this post and I am glad that TrueNAS is available to us.
But I feel the same way as Protopia
So I will test my hardware and play a bit with TrueNAS in different configurations
and decide then which option i will choose (probably not 2. Fork TrueNAS)