As much as I'm not really into Xbox's "Series" - generation-less undertones - this is quite an interesting pitch in isolation of xbox IMHO.
The rumoured technical specs probably undersell Lockhart capabilities, because I would expect it to share technologies beyond the RDNA2 of the GPU with the XsX.
So even if it is only 7.5GB RAM (of maybe 10GB?) available for games, I would wonder if that entire amount is clocked and connected to the same memory controller lanes as the fast portion of XsX at 560GB/s? If so, then clearly the bandwidth difference between the larger RAM of the X1X would give Lockhart an advantage; especially if coupled with the Velocity Architecture, that I would assume will be paired to a hybrid SSD containing at least 100GB of SSD buffer, and the XsS still supporting full XsX SSD expansion cards direct to the VA I/O system.
With more aggressive BCpack compression on Lockhart at 1080p, there could be a scenario where the X1X version of games looks downgraded, but the XsS and XsX have similar IQ when compared on smaller HD screens, along with XsS having similar loading times.
As much as people will laugh at the 4TF, the equivalent 6TF in GCN for X1X (or lesser amount on PS4 Pro) is still very serious hardware IMO, if used to its full potential - for more than upscaling X1 and PS4 visuals, and if Xbox can successfully get multi-plat devs to cater for their series of devices, then within Xbox's yardsticks for success this might work well for them.
I still believe in generations of hardware, but if this helps Xbox to have a market to still keep making games that impress, then hopefully it works for them.