tamarind8, if it's any comfort for you I think a similar situation is quite common in the industry. It's just that not may developers talk about it when it happens, rather they are sort of shamed into thinking that somehow they are inadequate. The _only_ measure of your output is the results you deliver and the time it takes. What tools you use is irrelevant. If indeed you were talking too long to deliver, reasonable colleagues would have asked you to try a different tool set. The situation that you are probably facing is that they do not like you (for what ever reason, even if you are not responsible for it, for example you don't fit in to their old boy's club), and when people do not like you they will dig up anything and everything that they perceive is a drawback in you.
From what you have said you are certainly not a junior dev. Where I see you being somewhat naive is exposure to toxic work environments. A large number of devs and their managers are just immature and nitpicky. Somehow a technology stack is a religion for them. I personally do not know anything that will satisfy such people. And then people can be unimaginably evil, something that often escapes the typical naive engineer/dev who often do not discover it even after having worked up until retirement. Like others have mentioned you have probably dodged a bullet. And your 3 weeks gap is barely anything. Often people can have larger gaps between jobs. Sometimes you can even cover up these gaps by lying on your resume. So point being, relax, do what you can and move on....
From what you have said you are certainly not a junior dev. Where I see you being somewhat naive is exposure to toxic work environments. A large number of devs and their managers are just immature and nitpicky. Somehow a technology stack is a religion for them. I personally do not know anything that will satisfy such people. And then people can be unimaginably evil, something that often escapes the typical naive engineer/dev who often do not discover it even after having worked up until retirement. Like others have mentioned you have probably dodged a bullet. And your 3 weeks gap is barely anything. Often people can have larger gaps between jobs. Sometimes you can even cover up these gaps by lying on your resume. So point being, relax, do what you can and move on....