I haven't seen any actual evidence to suggest Trump isn't actually a billionaire, first things first.
Otherwise, what a joke. Bloomberg is everything Trump claims to be-- a self-made entrepreneur, someone with a net worth in the tens of billions and (still!) rising, a generous philanthropist, a successful politician, in-demand in the most rarefied parts of Society. Bloomie has done everything Trump wishes he could, so he's left to knock Bloomberg, like a child, on the only thing he can-- his height. I bet every night, Trump goes to sleep wishing he was like Bloomberg, Buffett, the Kochs, Li Ka-Shing, and so forth; that he lived up to his own hype.
Bloomberg's last term as mayor was the exact opposite of a disaster, and if he actually ran for Mayor again (which he could, given that NYC term limits apply to consecutive terms) as I dearly wish he would, he would handily defeat de Blasio in a rout.
Well, for one thing, Bloomberg's own Billionaires Index estimates Trump's net worth to be $3 billion. As for the rest I would agree with you on many points. Trump's business prowess is not in the same league as people like Bloomberg, Buffet, Li Ka-Shing etc etc. And yes, I mostly backed a 3 Bloomberg terms which now seems like paradise compared to the disasters under de Blasio.
BTW, Bloomberg Billionaires Index has the following breakdown for Trump's net worth
Golf Courses and Resort Properties $710.0M
725 Fifth Avenue $600.0M
Vornado Partnership $590.0M
40 Wall Street $540.0M
6 East 57th Street $520.0M
Other Properties $220.0M
502 Park Avenue $170.0M
Cash & Other Assets $170.0M
Aircraft $65.0M
Washington hotel $60.0M
Misc Liabilities $-630.0M
This most likely underestimates Trump's net worth as it does not include goodwill. If Trump's assets were part of a publicly traded company then the trading value will be higher than book value which would boost his net worth some more. Forbes's $5 billion estimate take that approach instead of the Bloomberg book value approach.