Yeah, it's a really fun set of tradeoffs to play with. You're correct to a first approximation. Channel bandwidth is is easier to come by at higher frequencies (a 20MHz wide channel at 150MHz would be a giant swath of the band, but a 20MHz channel at 5GHz is very small relative to the centre frequency).
But... then you start encountering higher path loss. To make up for that, you need to increase transmitter power (whether by increasing actual power, or by using higher gain antennas, etc) or by adding redundancy to the data stream (e.g. FEC). The added redundancy chips away at your bit rate, but corrects errors.
In practice, whether you get a better net transfer speed on a narrow lower-frequency band or a wider higher-frequency band is going to depend on a lot of factors. Sometimes it pans out, sometimes not.
Small rx, small tx: low frequencies are better (lower loss).
Small rx, parabolic dish tx (or reversed): frequency does not matter.
Parabolic tx and rx: higher is better.
Small here means something like resonant dipole, so the antenna has to be physically bigger the lower the frequency.
For the case of a parabolic dish, we hold the diameter constant vs. frequency.
Anyway for phones lower bands are better as long as the antenna fits.