But what if someone like Wessex managed to take most of what we would call England? Would that result in Sexland, which is by far the best name for it.
Isn't what happened OTL? I mean, Wessex did dominated and absorbated other Anglo-Saxon kingdoms, after having defeated Mercian overlordship in the IX century.
Maybe migration patterns change. A majority of Saxons come to Britain while most Angles stay in Holstein.
Why? The climatic changes and pauperisation of germanic societies touched as well (if not much) Angles as Saxons. Admittedly, you could end with a neighbouring people defeating and assimilating Angles, but you would have changed Angles migrations with *Jutes or something else.
Admittedly, with less Northern-Western Germans migrations, you would end with a greater Frisian/Jute importance (Procope ignored OTL Angles to name Franks and Frisians after all).
I think you didn't get the main reason why Saxons and land they settled weren't named only as Saxon-Land : there was an original and still important Saxony on the continent, and differenciating the insular divided kingdoms looked like a good idea even then.
If not "Angli Saxones", you could end with "Frisii Saxones" or even "Britanii Saxones" if you end with really pedentic clerks.
Eventually, the most distinctive part is likely to be retained or at least something indicating these are "particular" Saxons. Bretland would be a relativly likely possibility (but appearing quite late and as said, under the influence of religious and clerical elites), while a Saxon-based name could be admittedly be used for the southern part of the island (Sessland by exemple, or Sessia).
The Great Heathen Army probably wouldn't be born, as Aella (?) king of Northumbria would not exist, his family still on the continent. Some time later, the vikings settled in northern France, now known as Normans, invade Sexland. Saxeterre to the Normans?
A pre-Great Migrations PoD is likely to butterfly all of that. North Sea peoples would be virtually unrecognizable.
One exemple among many possibles, stronger Frisian presence in England would make their political and economical disappearing in the VIII (due to Frankish conquests OTL) far less likely, at least because their christianisation became a more probable outcome.
Without Frisians out, the North Sea economical control wouldn't be that much a vaacum, and Norses would have an harder time imposing themselves.