I think this is a huge part of the problem. Rental property owners are just a liability buffer for the banks. There should be mortgages at a 1% down payment for first time buyers with a proven track record of making rent payments on time. Maybe the rates are a little higher, with the extra interest giving the banks motivation for taking on the extra risk. Then after the first term the owner can renew with a normal rate.
Doesn't help with the demand issue, but maybe all the rentals will flood the market after nobody is being punished for not having $100k laying around because they're busy paying someone else's carrying costs.
Yes, but also no. There are a bunch of other factors that contribute to a windows performance; manufacturer, type of gas used in the cavity, spacer material conductivity, thermal bridge free frame design, low e coatings and solar reflectance, and the quality of the installation matters most. Then there's the windows efficiency relative to the rest of the assembly. If it's a building code basic 2x4 wall from 1970 then you're absolutely right, it would be overkill putting some triple pane krypton filled window in. But if you've got a foot of exterior insulation and are pushing a u value of 0.13 on your wall assembly then you need windows to match.
Source: certified Passive House designer, the most demanding energy standard for buildings available, that originated in ..... yup you guessed it, Germany.