Bug Smash -- I readily concede you may be right - that slipping larger aircraft for glide slope enhancement just doesn't matter as an airframe life-limiting issue, but ONE detail is a source of concern:
Tail strength, etc are related during design to anticipated max crosswind speed for a given aircraft. However, no clear principle limits forward slips to the max angle implied by max crosswind speed. When slipping 'for effect', one tends to want to crank it in hard to get the 'feel' and then back off somewhat for tuning the result.
Done some distance above ground and at the pilot's discretion, a controllable fwd slip could quite possibly present an angle to the relative wind of TWICE what the max crosswind landing will do. Furthermore, this will be happening at velocities well above touchdown speed.
So, given that aerodynamic loads often increase at the cube of the airstream (vector) velocity, in fairly normal slip speedbraking one might be looking at 4x the tail load of a max allowed crosswind manoeuver - and that is before increments for turbulence and handling induced load factors.