The tricky bit goes Hirwaun, the west side of Aberdare, over to Meardy, back over the same climb, and then down to Mountain Ash, cuts over little roads to Ferndale. The shortest way back is then to Treorchy to retrace steps to Maesteg.
I lost trust in Strava's climbing figures when looking at Zigzag's log of the rides we did in the Alps last summer. It was very easy to find the total climb from topographic data (the bottom height in the valley subtracted from the height at the top of the col) as we were either going up for a very long way or down and no middling bits. Strava's figures were always 20% higher than reality and sometimes as much as 30%. The Cambrian series rides are calculated based on contour counts (which can understate climbing in rolling terrain and miss out those little kick ups and downs in valley roads).
I have, I think in this thread warned people who rely on GPS, especially Strava data, that they will record more climbing in the Cambrian series events on their devices than the measured amount. I did once do a route which genuinely had 3700m of ascent in 108km. Le Bourg d'Oisans - Alpe d'Huez, Col de Sarenne, Les Deux Alpes, D211A (that's the crazy road at the top of the cliff that joins Alpe d'Huez at Garde d'Huez), Le Bourg d'Oisans, Villard Notre Dame, Col du Saulude, Villard Raymond, Le Bourg d'Oisans. Neither Zigzag nor i are known for our hanging around although we did spend an hour for lunch in Les Deux Alpes, and it took us 8 hours to do the distance. To put it into context this is 6.7% average gradient up and down the whole ride.