Yes, the library used DMA and can refresh the panel data without directly involve the CPU, it used only to initiate process. So the loading of the CPU depends little on the screen size and is mainly determined by the refresh rate. For RP2040 board the CPU usage will be about 3% on 100 fps update and near 5% for 200fps.
The interrupt interval also depends on frame rate. The library uses BCM coding for colour levels therefore interrupt interval is variable.It base value for 200fps rate is 40us.
Of course, the low colour depth puts the library at a disadvantage. However, 8-12 bits per channel is not always needed. For info-boards and pointers, size is much more important. With the exception of colour bpp , it seems to me that the library features is quite at the level of similar libraries for the esp32 boards 
Of course, the Teensy core is much more powerful.
By the way, the library has its advantages. Support for outdoor multi-row matrices ( like 32x16 2scan, 32x16 4scan or 64x32 8scan) is not a problem and mostly included in base code. As I already wrote in the other topic, due to the non-standard pixel order in the buffer , outdoor matrices can be connected into daisy chains just as easily as regular panels.