service or not?

[MERMOZ]

hello!
i am new here so indulge a brief introduction.
55 and from belgium. bought my first rolex (gmt master II pepsi) 28 years ago. i started collecting them some 15 years ago. now i have 10. i bought all my watches new and own exclusively “sport” models. in total, i have a good 25 “quality” watches ranging from panerai and breitling to zenith, frank muller and audemars piguet.
i do NOT consider myself as a specialist, just an enthusiast.
i have asked myself long time the question which follows and which i will try to formulate in my weird logic. please forgive if the question has come somewhere else in the forums…
unless the obvious when a watch has a piece damaged in the mechanism and it stops or has a crazy behaviour (it happened to me), to me the only reason to service a watch is to have the oil changed. “if all the metal is ok inside, why open a watch?” is my idea, if you wish.
contrary to a car engine, the oil inside a watch “only” lubricates the metal to minimize friction or better said to make forces in presence equalize with friction in order to give accuracy (in a car engine, the oil evacuates the heat and burns -> it degrades “quickly” and has to be changed, no option).
that in mind, i follow the reasoning: if friction is ok, then oil must be ok, meaning not dried out.
how do we know if friction is ok then?
just simply by measuring watch accuracy in time keeping (the measure itself has to be accurate!).
so, if a given watch moves by, say, 3 seconds per day or even variates from, again say, -5 to +5 seconds per day and never increases above, then the watch is steady accurate.
then the friction is ok.
then the oil is ok.
then there is no need for servicing.
please your thinking.
if there is a flaw in my reasoning, don’t shoot.
many thanks.