A simple calculation shows you need an enormous volume float to generate a useful amount of power. A tidal range of a few meters isn't that much potential energy applied to a float of limited volume: by contrast, there is much greater mass of water in the sea to generate energy from.
An object displacing 250kt of water (ie. size of Ever Given) has a potential of about 0.7MWh per 1m. Most coastal regions see tides above 2m and a lot much higher than that.
I say 1MWh extracted daily from from a dumb metal object the size of Ever Given (and potentially much more if you are in are with exceptional tides)?
I guess it would depend on how efficiently it can be built and the cost of additional infrastructure (though it would be less if you build it in form of a farm).
Remember, it can be used as energy storage, so if you have a large farm you can program it to automatically pull some of the containers deeper to provide power when at low tide.
Also efficiency of this can increase with the size of the tank as the amount of materials scales less than linearly.
I used Ever Given as an example, but this has been built to be seaworthy and pass Suez Canal. If you don't need to make it seaworthy and don't need to make it to pass through anything and can make it any shape you want you could probably design much larger structure.
Consider a single offshore turbine in the Galloper wind farm is rated at 6 MW and this doesn't look so impressive.
> a dumb metal object
That's the thing. It isn't a dumb metal object. It requires generating gear, maintenance and protection from weather. Also consider the Ever Given is 1/4 mile long. These are big volumes you are talking about.
No matter how you look at it, wind is a tough candidate to beat when it comes to offshore power.
The fancier the installation, the more money needed by specialist humans to keep the thing running.
Offshore wind at scale is pretty affordable and less "fancy", relatively speaking.