You are right that if it has even just one dead glow plug it will make cold starts a little rocky and smoky. However, lack of timing advance and/or loss of fuel pump prime after sitting, due to leaks, can have the same effect, so more troubleshooting would be required to know what is at fault for sure.
Note that there are two separate (although related) functions of the cold start system: 1) advancing timing and 2) raising idle speed. They both work on the motion of the same lever, but the timing function (1) occurs internally inside the pump based on the rotation of the shaft that the lever is attached to, whereas the idle boost function (2) works externally, based on the contact between the cold start lever's ball stud with the tab on the bottom of the main throttle lever.
Hence, some adjustments you might make would affect one function only, whereas others (such as changing the setting of the cable) would affect both.
If the cable position didn't change, and the only thing that was moved was the ball stud, then the timing advance part (1) should still be working as it was. That is good since it is the more important part. The idle speed increase (2) is controlled by the position of that ball stud and it sounds like that is not having as much of an effect as it used to, but that doesn't matter as much.
That said, if the engine power is still weaker than it used to be, plus worse MPG, plus difficult cold starts, plus fuel leaks, then I agree a return trip to your diesel mechanics would be a good idea. Maybe tell them this time you do not want to pick the car up until it is 100% right and they can take whatever time they need to repair it fully.
And once more, consider the idea of having the pump fully resealed and recalibrated. This will cost more, but you would only have to do it once, and when it goes back on the engine
(assuming timed correctly) it will run precisely like it's supposed to and no more fiddling will be needed anywhere. Cold start timing and idle increase settings will be exactly right, power level and response right, etc. And with the pump removed you can also easily access #5 and #6 glow plugs for replacement if that is needed. Up to you but this is the way you could do it that would solve all issues in one fell swoop.