Hi @anon34731316,
Damned!
You were right, this was due to the overridden route router.get('/users'...
I am so sorry for that mistake.
But it is due to a specificity that I coud not guess on the use of recordsGetter.serialize function.
I opened a new issue (please see performance issue #1010) to avoid mixing subjects.
Please see it, as it is generating the issue that I described here.
Now, with the standard routes, I agree with you: the useless smart fields of associated collections are computed when accessing the records detail.
Thanks for fixing it as soon as you can.
Best.