Wrong type mortar used??

The fact that he hadn't used lime should not be detrimental to the building and to use a grinder is not good practice for racking out joints as it's not that accurate as you have found, the only issue would be the ascetic appearance of the finished job certainly in the case of a terraced property, I trust it's not listed or of local interest as the appearance could case an issue, however, providing it's had been well tucked into the joints it should not cause any issues structurally just the appearance. However one needs to ensure as any mortar no matter what building it is needs to be weaker than the brick to allow for thermal movement and drying shrinkage. As the added note states that the house is of cavity construction and trusting there is no problem with damp egress, looking at the data sheet for a Accrington brick being low porous and weathering in my 50 years plus dealing with brickwork I stand by my earlier conclusion,

lime mortar allows your building to breathe, this type of house was designed to allow any moisture getting into the structure to wick out the mortar lines when dry out side preventing dampness,also allows the building to move without causing any issues, cement is to strong & seals the building trapping water behind the cement, any cracks created by movement allows further water ingress behind the cement creating dampness, unfortunately today tradesmen work with modern material which do the opposite so do not understand how the materials used in the construction of your property all work together to keep it dr. look up the heritage property web site also look at lime mortars renders plasters to understand how these materials kept your house dry. It really up to yourself what you do but if you start getting dampness you now know why. Dampness dissipates at the rate of 1 inch per month so it takes a long time to dry out if it has a cavity the cavity will stop water transfer through the brickwork providing it has not been filled by cavity wall insulation good luck Alex

I would have to agree with Alex here. Modern cement based mortar is not breathable, if your house is of a certain age and has solid wall construction as opposed to cavity walls then cement mortar is the wrong choice, lime mortar is breathable and helps to prevent damp.

The size of the joints shouldn't matter , but on old houses lime must be used as it allows the house to breath and expels any damp.