In simple terms, IMO it's like taking a Boardman Hybrid road racing... Yes the Zesty will be fine... yes the Zesty will cope.... but.... and it's a big but..
It won't give you the confidence and speed a more appropriate bike will. Instead of it being you that's the factor holding tthings back, it will be a combination of you and the bike.
When we went i took a 170mm Bionicon, i was quickest to the bottom of all the sections going down.
My mates were on a zesty and a stumpy... they're both superior riders to me... but the bike meant i got down quicker/better/easier.
Why go all that way and end up getting frustrated because you're on the ragged edge all the time and your mates are strolling down ahead of you with ease.
I have no doubt Steve Peat could get to the bottom quicker on a Halfords HT than i can on the 180mm Scott i've hired for this year... but i'm not Steve Peat, i will be quicker, have more pleasure and feel safer on the 180mm Scott ... simple as that.