Bro you are right, but there is also another side of it.
Rightly said, but it can also expose seals and leakages from those seals, especially in case of older engines or high odo reading (although seals were already deteriorated. The sludge / gunk which had developed had concealed them, and via engine flush, they get exposed).
I am not saying to use engine flush every time. Just for the first time and for once, when you are changing engine oil grade / viscosity / brand, I would suggest it (so as to remove everything of the old oil). Different brands have different detergents, formulas, and other chemicals, etc. so when you flush, you are sure that nothing from the previous oil brand will interfere with the new engine oil brand and grade.
Not true all at! Almost all the engine flushes from reputed brands are safe. There are even some reputed brands which recommend engine oil flush with every oil change (although I personally think that its a waste of resources & money). As an example: AMSOIL Engine and Transmission Flush is safe enough to be used at every oil change
(Source of this info and more details about the product: https://www.amsoil.com/shop/by-product/other-products/cleaners-and-protectants/engine-and-transmission-flush/?code=FLSHCN-EA )
More info about engine flushing can be found at:
https://blog.amsoil.com/is-an-engine-flush-good-or-bad/ and https://thegaragely.com/is-an-engine-flush-good-or-bad/
I hope, it all helps. Thank you.