Can the decision to change jobs, despite feeling uneasy after performing Salatul-Istikhara, be a wrong and counterproductive decision, especially with the feeling of severe distress and regret?

Since you have sought Allah’s guidance (istikhara), you should be content with what He has decreed and predestined, for there is good in it that you do not know. You must submit to Allah's judgment and entrust your affairs to Him. If you wish to leave your job, seek Allah's guidance (istikhara) and consult those with experience, then make your decision, accustoming yourself to be pleased with Allah's decree, for whoever seeks guidance and consults will not be disappointed. If leaving it is not an option, then accustom yourself to be content, and know that it is good for you as long as Allah has decreed and predestined it after your istikhara.