OP:
* There is no one correct mount for all skaters; each skater's feet are different. What your skate tech did is insane. The logical sequence is to first mount the blades with a so-called temporary mount. The sole plate and the heel plate (on each blade) each have two elongated mounting slots (what you are calling "sliders"); the remaining mounting holes are all circular. In a temporary mount, screws are installed in the elongated slots only. This does allow only a small amount of adjustment, which for some people is sufficient. If more adjustment is needed, only four holes (per boot) need to be plugged, and only four new holes need to be drilled. With problematic feet, this process may need to be repeated. Once you've established a proper temporary mount, the tech will install more (not necessarily all) screws in the circular holes to create the so-called permanent mount.
* If you are lucky and the mount works for your feet, no harm done. I hope that's the case for you!!! If you are not lucky, the tech now needs to plug 14(!) holes per boot. And redrill new holes. Think about that. If that should be necessary, Edea boots require special carbon-composite filler plugs and adhesive. I hope that he doesn't charge you for materials and labor for installing the plugs, if that should be needed (he shouldn't if he's decent).
* With traditional leather soles, it is true that if a prior mounting hole is slightly stripped, sometimes (not always) you can re-use the old mounting hole by using a larger diameter screw, without the need to plug the hole first. Traditional leather soles use standard sheet-metal screws, which are readily available in a variety of diameters and lengths. Edeas, however, use thinner, carbon-composite soles, which require custom Edea mounting screws. And, as far as I'm aware, they come only in one diameter and length, so that option is not available.