have you tried outlasting him instead? use embers to ember tap ,use shadowfury into fear to force the first trinket, howl to force the tremor,he has no ways to break fear for another minute,simply play the turtle playstyle ,heal up via embers,use defensive cd and regen/HS on ascendance.
Once shaman goes low anticipate the grounding ,remove it and silence his heal,u can win just use abilities in a smart way.
Ofc u can win with cbs,u just need to build enough embers then setup a cc chain to burst ,like after u make him waste his tremor/trinket, and if u have like 2-3 embers,Fear->pop cds/first CB->shadowfury->second CB ->silence->3rd CB->fear->finish,or something like that,I know this is just on paper and its easier said than done,but u can manage as a lock I assure you.