Firstly, the Me 163 is classed as tailless, not semi-tailless. The fin does not count.
Secondly, its characteristics were not wholly benign but they were acceptable by the standards of the moment for a high-speed fighter. Its lateral stability was marginal and it could behave unpleasantly in the stall. When Junkers developed it further, they found it necessary to make the leading-edge slots automatically variable and to increase the area of the landing flaps. But on the whole, yes, it was better than most tailless types.
So, why was this particular plane adequate? You will have to bear with me. A long trail of aerodynamic refinement begins with JW Dunne's tailless swept monoplanes and biplanes of the pioneer era. His D.10 biplane became the first aircraft ever to be officially certified as stable. The finless monoplanes could at least be stalled, but simply pancaked down rather than dropping a wing. Around thirty Dunne machines were flown in the UK and US and none ever had a fatal accident, a staggering safety record for that era. Dunne's secrets were many and subtle, expounded to the Aeronautical Society of Great Britain in 1913.
In the 1920s an ex RAF Captain, GTR Hill, took up the unstallable challenge once more and refined Dunne's aerodynamics, developing among other things the mathematics of the constant centre of pressure via reflex camber. A German visitor whose name I forget took it back to Germany where it was further enhanced and there Alexander Lippisch discovered it. He had the luxury of ten years' single-minded research and experimentation on one prototype after another, from glider to propeller to rocket, until the Me 163 emerged. But neither Hill nor Lippisch could get rid of the fin.
Meanwhile the detailed technical work of Dunne received only voice plaudits from others, while that of Prandtl in the early 1930s went unnoticed. Reimar Horten trod the path for himself to arrive at the finless Horten/Gotha flying-wing fighter which also handled well but came too late for wartime production.
What Dunne intuited and tested in hundreds of models, Lippisch half-grasped and Horten rediscovered and calculated, never made it over to Northrop or General Aircraft or any of the others. When Dunne's trademark conical leading-edge droop was rediscovered and used on the Convair deltas to make them flyable at low speeds, the path to it lay through quite another labyrinth. Back in the UK, Dunne and de Havilland renewed their old friendship, for DH had been Dunne's successor at Farnborough and both had trod the corridors of the RAeS together. DH wrote to Dunne that during the development of the DH.108 he would tease his staff that Dunne had got it right all those years ago, so they better had too. But like Lippisch, even he had to keep the fin. And despite also being informed by both Lippisch and the Hortens, his DH 108 was described by one test pilot as "malignant".
The real questions must be; why did so many designers turn a blind eye to the tailoring of span loading and sideways flow to eliminate adverse yaw and the need for a tail fin? and how did they manage to introduce appalling stall characteristics when Dunne's original breakthrough was to tame the stall? The key lessons had been in print since 1913, for those who had eyes to see, and Horten at least had proved capable of finding them for himself. Simple ignorance, preoccupation with conventional design issues and "not invented here" are my best guess. Prandtl's and Horten's contributions are only now beginning to receive wider acknowledgement. The epilogue must go to General Aircraft, whose GAL.56 was described by the ubiquitous Winkle Brown as the most badly-behaved aircraft he had ever flown, before it went on to kill the most experienced tailless aircraft test pilot in the world and who had consequently flown many Lippisch creations, Robert Kronfeld.
For those who want provenance and more detail I fear that you will have to wait until I can get quite a backlog of stuff past our Covid-coma'ed publishing industry. Or you may tread the Science Museum Archive's Dunne Collection for yourself, all 30,000 documents and boxfuls of artefacts of it.