Ws2812 has a fixed data rate, so you won’t be able to push tons of pixels with high frame rate on a single data line. 800Kbps, at 24 bits per pixel. 33k pixels a sec max. That’s like 16 FPS theoretical max if rendering was instantaneous. Next is the implementation of the LED driver. Ws2812 is very picky about timing, so the engine waits for sending to complete before rendering again (avoids glitches).
Other led types like apa102 can be asynchronous, as is the output expander so rendering can happen concurrently and FPS are higher even taking data rates into account.
The expander handles up to 66k pixels a second, and sends data out in parallel. It could easily help improve fps just by splitting you pixels on 3-4 channels.
You can experiment with FPS by changing the led type to output expander, add a board, and configure some channels. From PB’s perspective it doesn’t know you don’t have an expander attached and your FPS should improve.