i guess CX needs to offer some benefits to each category - if SL doesn't offer lounge access (when flying on CX/KA economy), then it's really not that much different from GR apart from 10 kg baggage and priority baggage.
keeping lounge access for SL is quite fair. i was lured from GR to SL because of lounge access. then got lured to GO (don't really know how that happened) ... and now to DM!