I'm not sure what you're looking for exactly, just buy a monitor. We do Smart TV app development across a variety of platforms (Smart TV's, Rokus, Xbox) and the vast majority of this development is done on off the shelf 24" Monitor's with HDMI inputs. We joke all the time that the cheapest TVs are in the monitor aisle. (This is only true to a certain size however)

I should note the LG TVs in the OP are actually great test machines too...

Why not just buy a regular computer monitor then ? The lack of large screen sizes ? This I can understand.

Perhaps consider buying a commercial display then. Not only do thye lack tuners, but if there is an ethernet port, it is most likely there for you to use to remote control the display. The only downside is that they typically cost a bit more.

The example you picked, Vizio, is the lowest-end brand on the market. Nothing wrong with cheap, for the price you pay, but the whole point is that it cuts corners and isn't as good as the name brands.

Unfortunately, this isn't free for the manufacturers, and most people are not going to want to spend the same (still less, more) on a TV with fewer features -- even if they'll never use them.