You may yet prove to be right, but until the timetable has actually had a chance to fail on its own terms I don't think a judgement should be made. The service since the timetable changed has been awful, there's no doubt about that, but it is largely due to 2 issues: general shortage of drivers, which has been going on for years, and secondly and more importantly: GTR not training enough drivers for the 700s. Once these issues are sorted, particularly the latter, we will be able to properly judge through running. I don't know if it'll work.
My opinion is it probably won't because a signal fault or fatality etc south of the river will cause massive problems. However, I'm open minded enough to wait and see. I've never been sure about running Peterborough and Cambridge trains through the core. I would have liked to have seen WGC/HFN-core or long distance stuff - Kings Lynn, Lincoln, York. Having said that running WGC/HFN away from Moorgate causes two issues - what then runs into Moorgate, and there is no extra freed up capacity at Kings Cross. If IC services were run through then they could be severely impacted with delays especially given their infrequent service. If the line was new build, with limited outside interaction then both of these options would be preferable, but unfortunately it isn't. To sum up, I think we've probably got the best compromise as it ticks boxes of longer trains, more capacity, higher frequency (in places), gives passengers options for changing to the tube, and creates capacity at Kings Cross.