I think it’s a good idea to include hitsounds from the beginning since it would probably be added by a mod anyway; this way at least SD can balance the weapons with hitsounds in mind.
Regarding accuracy before hitsounds: not impossible, but better audio/visual feedback when you hit someone does help you learn where to aim, especially when antilag and hitboxes are less than perfect. The “probing” through smoke in W:ET is an unfortunate side effect, but they may be able to prevent that in ET:QW if they want to.