There's a number of issues.
When I said about Q1 having fast turnon and turnoff times, they should be vertical. Your first diagram shows Q1 turnoff (0v-5v transistion) is very slow, taking maybe 12% or more of the total cycle time. That's really poor in terms of efficiency.
I think this is partly because freq is too high, looks like about 11uS per cycle or 91kHz, if you can drop this to 20kHz with the same imperfect turnoff time then you have 4.5 times less switching losses. The freq is probably high because of removing C2, which is the main RC delay component that slows the circuit down and improves efficiency.
In your second chart (Q1 Ve) you can see the R2 voltage, which should rise until it reaches about 200mV and causes the turnoff to begin. This is not happening, because turnoff is starting about 4mV I think you are getting the old problem of oscillating based on Q1 saturation prblems instead of the desired oscillation based on R2 current >setpoint.
I would start by removing the zener, and setting a higher value R4 until it oscillates at a point where R2 (Q1 Ve) reaches 0.2v. And also with a large enough value for C2 so that oscillation is 20-30kHz. At that point you will be putting max current to the load resistor so choose R2 value to give the max desired current into the load.
You might also need to replace the resistor that was originally where Cfb is now, that resistor keeps Q2 turned on for the duration of the flyback pulse, which decreases frequency.
Have you worked out a desired max output current yet? Your R2 value of 1 ohm , switched at 200mV will set output current of maybe 100mA, which seems high to me.