Question about Makita Rt0702cx2j

No, it is not suitable for that. It is possible to make grooves in various shapes with a router. The router works with a rotating (finger) cutter that is clamped vertically and then plunged into the workpiece like this. A flat dowel router (such as the Makita PJ7000j), on the other hand, has a small, horizontally aligned saw blade similar to a circular saw and "cuts" the groove for the flat dowels by "plunging" the saw blade into the workpiece. The flat dowels then fit exactly to the thickness and the milled out shape (oval) of the groove made.