I cannot say that I have seen anything that indicates leaving 30% of an SSD free leads to optimum performance. As far as i am concerned it may or may not be true but in the greater scheme of things, based on empirical experience, I don't think that it is important.
I have two MBPs that have 1 TB SSDs that are both 85%+ full and and I detect no adverse performance symptoms. I am inclined to believe that we are dealing with 'a law of diminishing returns' at best. Prior to the installation of the SSDs, I had 1 TB HDDs with one MBP having about 950 MB of data. No detectable performance decline was observed and I suspect the '15% free space rule of thumb' really does not exist for HDDs. That may also may be the case for SSDs but I cannot say so with authority.
If you enable TRIM or allow for 'Garbage Collection' your SSD will perform satisfactorily. My unfounded view is that the differences between a SSD with more than 70% of it's capacity used vs. one with less than 70% of it capacity used is in terms of real world usage going to be virtually undetectable. We may be dealing with differences that require measuring devices to demonstrate such differences which may be very, very small.
It may be analogous to bench test scores of two macs that have similar scores. There may be score differences, but when actually using them, you may not be able to tell which is that 'faster' Mac.
Ciao.