Every system is subject to gaming of course, but I think taxing assets would make it a little harder for companies and individuals with lots of assets to avoid taxation and would encourage putting money to work.
Values for assets are market values, which are arbitrary and every-changing yes, just like income and profit is arbitrary and every-changing but at least values for assets are generally set by third parties, as opposed to the value of profits - the situation could not be much worse than the one at present where large companies choose how much tax to pay by manipulating their books to adjust profit.
I don't think companies should be taxed on customers personally, but if they choose to value their brand name at $10m owned by a subsidiary as a tax dodge (as at present), sure they should be taxed on that.