We need to ask ourselves some questions before:
[1]
Is this really a problem today, and slowly QET, or element editor, I don't know?
In 2015, yes with Qt 4 and no UUID, because computing power was very limited 32 bits, one core CPU, little RAM on setup, and QET launches took a very long time, even though there were far fewer symbols in the collection.
Maybe can be affect element editor in 2015 year's.
Since the upgrade to Qt 5X, Qt has been storing XML attributes as a lottery, which means we've had to do a lot of work to make QET faster.
[2]
Copying and pasting primitives from several elements is very useful and I've used it a lot to create new symbols from scratch.
[3]
As long as the clipboard copy doesn't involve rounding off the primitives pasted, there's no point in wasting time writing a batch script to correct the collection until the source of the problem has been found and solved...
[4]
QET_element_Scaler round primitives to two decimal when scaling, mirroring or flip the element?
DXf2elmt round primitives to two decimal when converting a large DXF into an element?
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BTW, One of the priorities that I think is essential would be this:
https://qelectrotech.org/forum/viewtopic.php?id=2486
And maybe add new type and drawning contact for start delay star triangle, like LADS2..., and pre-break contact disconnector ?
pre-break contact disconnector