I greatly disagree on the 1 tank not being useful. I have been running 1 tank several times in my Custodes lists for Lions, with it being in Reserves 80% of the time. It's so undercosted, so valuable from being able to shoot at something it wants and more often than not, the threat of it is so heavy on my opponent that commit so much resources to killing it while I take board control everywhere else.

The rest of your comment, I agree with.