You might as well say “Our old website was so crap that we couldn’t leave it up for people to see – so we put this bland landing page in its place which tells you nothing about our company”.
Is your old website that bad that you are prepared to lose customers and trash any Google rankings that you had? Your potential customers are not going to look at a “Coming Soon” message and say that’s OK we will wait – no, they will go to your competitors.
Just keep your old website there until your new one is ready.
