Advice Needed on Slate Roof Ridge and Stone Join

[HWW91]

Hi all

We have recently had a new roof constructed on our Victorian terraced property, which has been tiled with Eternit Slates.

When checking for snagging items we noticed the ridge stone join kicks up significantly and looks very shoddy due to the quantity of cement used.

I have never noticed any roofs with this quirk but the builder is reluctant to change it, stating this is how it should be by design, in order to best keep water out.

I suspect they have cut the ridge stones incorrectly and have had to fill the gaps with copious amounts of cement - ridge stone joins on other roofs I have noticed appear near and flush.

Can anyone advise?