PT stepping in here! My clients would often come to me with the whole fitness/smart watch predicament and this is how I see it (as someone that has been using a Fitbit and now Apple Watch for about 8 years).
At the end of the day, it's about consistency, and in this case (if you're dubious about the accuracy) 'inaccurate inconsistency'.
Okay so you might not
literally hit 10,000 steps that day, but if you use the same watch day after day for a year, you're going to get your own personal baseline and something to go by. Also, if the goal of hitting 10k steps gets you out and about, keeping active & healthy, it probably doesn't matter all that much whether it ends up being 9,000 or 11,000.
They can be a fun tool, but easy to get obsessed with, so if you think you may get fixated on the accuracy then it could just be that they aren't for you
I hope this helped somehow xx