I think it was perfectly fair. There have been plenty of other Listeners where a lot of cold solving was required before you could do much, if any, grid filling. I think I had cold solved ~60% and was able to fill in most of the bottom (the wiggles were really helpful), so I did not find it true that I needed to cold solve almost everything. In any case, cold solving may not be to your liking, but that doesn't make it unfair.
I would say, however, that if the theme is really the 5,5 phrase, then the final step is not thematic. Unless I do not understand (certainly possible) the theme is a two-word phrase (5,5); the unclued octagons consist of two synonyms for the first word (call them a1 and a2) and two for the second (b1 and b2). I do not see how a1 goes with b1 any more than it goes with b2; same for a2.
Then we apply the 6,5,5 match rule to come up with the 4 square entries - and I see no thematic connection (or really ANY connection) other than they are the only words that possibly result from the 6,5,5 machine.
So I think I would rate it very highly for giving us a quite difficult challenge that was very satisfying to solve, but thematically was somewhat lacking.