That does not make sense to me.
Yes both Unreal and UT were originally "made" with UEd1, but then they updated both regularly before the "end-of-life".
UEd was on v2 before the last official patches, so both have had a newer official Ed.
More content exists for both games that has been made in UEd2, than was originally made with UEd1.
If it was just the 1 product, we would still have had updates until they made the next engine.
I can't see why if they were limited to the 1 game they would decide not to update the tools they used until the next engine
The more versions they have, the less reason they have to update the older ones.
All this is fantasy.
In a hypothetical reality where UT would have been an expansion of Unreal, what makes you think they would have needed to update the editor, given that they managed to release two very good games with the old one? What makes you think they would have kept updating the game as long as they did? What makes you think "end of life" would not have been years?
Remember UT is on a improved build of the engine while Unreal is only build 220+. The fact that they updated the engine and the editor is largely due to the fact that UT was their top-line product for such a long time. If they had kept using the old 220+ builds for a combined Unreal/UT, why would they have updated the editor instead of keeping the 2.0 one for newer builds of the engine for licensees or for their new games on build 400+? Remember they never backported UEd 2.0 to Unreal; maybe it was too much of a hassle to do it, or maybe they thought the 220+ engine was too old at that point and they wanted to focus on new builds (which they actually did). Why would that have changed if UT had been just an addition streamline into Unreal's old build?
You could provide a very acceptable answer to any of these questions and I could give acceptable rebuttal to all of them. All this is just fantasy with nothing solid to back it up; as far as we know, they reached a stage where they decided a new editor was needed for their engine which had become much better than the old version used in Unreal. The facts are: Unreal had poor netcode which was overhauled for UT, it had a shaky editor which was overhauled for UT, an engine which was improved for UT, and some of these changes were backported from UT to Unreal. There's no telling anything like that would have happened otherwise.
Unless of course you have inside-knowledge, in which case you should write about it because any information about the sweat on cliffy's brow during the development of UT is welcomed
You must construct additional pylons.