I think my idea (or Henry George's) is right and would remove their earnings from land.
The bottom end of landlords who use negative gearing to obtain investments, Sure. It won't affect the higher paid professional couples, as those landlords would just pass on the tax in the rent. Ie. it is a meaningless tax to them, but is significant to their tennants (the tax gets passed to them to pay, through rent)
You lalso don't appear to have considered how much
land tax would have to be per year to replace the current system. The amount of tax, passed on (as all landlords will do) - I would suggest that it would be significantly more than the very poor currently pay in tax per year (because the lowest earners don't pay income tax due to the threshhold).
Further, the lowest earners still would not be able to buy a house (because they won't have the savings, and won't be able to get a loan from the bank), meaning they are entirely reliant on landlords for housing...who will pass on the land tax costs to them (I have to keep mentioning this because it leads to a major issue)
Further, the less well off professionals may well offload investment properties, which would in your scheme be snapped up by the better off poor...diminishing the rental pool in affordable suburbs (they still won't be able to afford it in good suburbs), which in turn drives up the rental price in those affordable suburbs (supply vs demand)
It is very likely your scheme would create a great deal more financial distress and homelessness amongst the poorest.