Is a 2.5mm parquet wear layer sufficient?

I would still make it dependent on the installation method. If it is glued and the ceiling is statically decoupled, I see no problem regarding sound insulation

Sorry please: The original question was based on the thickness of the wear layer of a multi-layer parquet in the context of a disadvantage.
So what helpful information is the aspect "sound insulation and installation method," picked up here out of context, supposed to provide to the questioner at this point?
Nothing - exactly!
Sorry for the blunt, but in my opinion justified words!

If a thinner wear layer results in an overall thinner parquet construction, it was merely an indication that besides the obvious aspect of the low number of sanding processes, possibly also a lower impact sound can be the side effect. This was then followed only by the remark that the side effect probably occurs more significantly with a floating installation than with a glued installation.

It was merely a thought of a layman. I also started my expression of opinion that way. I apologize for my unqualified, incoherent expression of opinion.

I found the objection regarding impact sound quite good. But isn't it the case that this is absorbed by a special mat under the [package]?

Isn't impact sound insulation a totally unnecessary thought anyway on the ground floor of a house? In the basement below (if available), no one cares about it anyway. Apart from that, I would always glue down parquet.

I wouldn’t sand floating parquet either. These sanding machines are very heavy and there is a risk that your parquet boards will come apart at the joints.

Best regards
Sabine