GFX lib with font, canvas, and drawBitmap() runs slow

[norbinz]

I breadboarded an Adafruit 3677 (ItsyBitsy 32u4 5V) with an Adafruit 4383 (240x135 LCD ST7789).
I'm seeing very slow run-time of the GFX library's drawBitmap().
In the Adafruit forum I asked what's the reason for the slowness, and does the library offer a faster alternative?
I shared a demonstration sketch that includes the slow drawBitmap(), and a faster code that I whipped up.
A support (?) fellow suggested that I ask on github.
Here's the forum discussion:
https://forums.adafruit.com/viewtopic.php?p=960409

I understand that the GFX lib has a Prime Directive, but I'm not sure if that applies here.

[norbinz]

Oops, broken URL. Trying again:
https://forums.adafruit.com/viewtopic.php?p=960155