Via stitching removes solid ground plane
Stitching vias are typically used to connect multiple ground planes on different layers together. Since they are connected to ground there is no break in the plane other than the drill hole which is negligible. Return current flows on the plane directly under the trace but spreads out some distance from trace with the strength of the field dropping off further away from the trace. Typically a distance of 3 to 5 times the width of the trace or dielectric height is used to determine spacing to an adjacent trace that will not result in significant cross talk. Although current flow is on the surface of the trace and ground plane (due to skin effect) the field is actually in the space between the two conductors.