Being Devils advocate here......
Most of us have to have some kind of cost consideration or everyone would have £2k worth of tyres.
Falken, Toyo, Vreds etc etc are all chosen because they perform well enough for your needs at a good price.
Running a lower profile has been done by several people successfully so if by changing the size that means they save a few quid or can 'upgrade' to better rubber then I personally don't seeing it as being an issue.
My advice would be to know what you are putting on. If you buy langyong tyre factory ditchfinder xls+ then that's fine but don't expect them to perform. If you want to run 40 profile then know the pros and cons before purchasing as it'll cost you twice if you get it wrong.
Anyway, that's my 2p.