Hi mate, sorry for late response. If you are feeling a major difference with the sensor disconnected, there should be something up with it. If you can, check the resistance value as well, it should help to make sure if the values are within specified limits. I have been riding around without the sensor connected for a while now and I'm pretty much happy with the bike. The difference was quite massive for me as well. This seems to be a common but undiagnosed problem in the 250s from the looks of it. The only solution for you unfortunately is to swap the sensor and observe the difference. It is not cheap at around 2500-3k.

I have checked the heater element it also shows the correct range.could you please explain the problem you had before the o2 sensor replacement.
In my case ,there is no idle hunting issue ,the idle is stable at 1500rpm after warming up procedure .
The issue in my case is poor throttle response in lower rpms it is more pronounced in lower gears.Based on some people this is usual for any vehicle which is tuned for bs6.when running in closed loop mode