I reckon MBR has more rocky sections. I remember Tarw having a few rocky sections but not as many?The Banshee Bikes Blog: Search results for sag
The stuff on the 'original' side (original start to MBR and Karrimor) has more armoured sections, not what I'd call rocky, just paving slabs lined up to make a hard wearing surface:
Flightpath circa 2004:
[url= https://farm1.staticflickr.com/30/37440318_3a2f2ffd11_z.jp g" target="_blank">https://farm1.staticflickr.com/30/37440318_3a2f2ffd11_z.jp g"/> [/img][/url][url= https://flic.kr/p/4iTGJ ]Julie at Coed y Brenin[/url] by [url= https://www.flickr.com/people/75003318@N00/ ]brf[/url], on Flickr
I don't know how to reconcile your various posts though, one minute the rocks are all new, little obstacles...
Possibly because I never thought of the older rocky bits as obstacles, just rode over it all without really paying much attention. They have made an attempt to add some new bits which look like obstacles i.e. a few steps in the middle of a bit of flowing single track, but they're hardly difficult and certainly don't need FS.
Here's what it used to look like before it was sanitised with paving slabs. This is the original Hermon:
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Photo from here: http://www.mtbbritain.co.uk/hermon_flyer.html
NB This is still new compared to the first routes there, which were all unofficial and came from a route guide in MBR mid 90s written by Dafydd Davies.