Is this how a R-2R DAC for VGA should work?

The bits you control are either On or Disconnected, while in general a R2R DAC input would be connected to 3V3 or 0V. Disconnecting changes the impedance. Try with SPDT switches.

This is how I would have made a 4 bit DAC on 5.000 V logic.

16 levels from 0 to 4.5V
300 mV per level. Then Buffer output as required.

1R= 50.00k
2R=100.00k
Term = 1.200M
Error = 0 with 300mV per step using trimmed Vcc.

for 3.3V Logic Term=1.6M then 0 to 3.00V max with exactly 200mV /step