This answer is in addition to xLeitex's answer, which deals well with OP's situation. I would like to add some general points, however.

• You have come out of undergrad or master's and are starting your PhD. This is a very different environment that requires different skills and caries its own challenges. Working among (hopefully!) intelligent, motivated and more mature people, you will find that standards are higher and attitudes are different - a bit like the transition from school to university. This transition often causes people a shock and results in imposter syndrome and similar issues. Almost all PhD students (apart from the sociopaths) will feel insecurity and inadequacy at some point during their PhDs (but don't expect them to show it!). Be prepared for this, when it happens!
• Generally, people are unlikely to judge a student's capability by their group. In fact, very often the best groups/supervisors do not produce the best students; the reason for this is that it's often easy for students in such groups to coast along on the backs of their supervisors and colleagues. When I think about groups I have worked in/with, they've all contained a huge range of students; some excellent, some barely passable. If you want to stand out, work hard, work independently and produce results. Be active in engaging in collaborations with other students/academics.
• Be careful about judging other student's work - that not for you to do. Be aware that differences in output are often caused by differences in aspirations and motivation that do not necessarily make a student "better" or "worse". For instance, a student that has decided they wish to leave academia for industry after graduation will have far less impetus to push out high-quality, high-impact publications than one that wants to stay in academia. This doesn't reflect their capability nor their quality as a student.

This answer is in addition to xLeitex's answer, which deals well with OP's situation. I would like to add some general points, however.

• You have come out of undergrad or master's and are starting your PhD. This is a very different environment that requires different skills and caries its own challenges. Working among (hopefully!) intelligent, motivated and more mature people, you will find that standards are higher and attitudes are different - a bit like the transition from school to university. This transition often causes people a shock and results in imposter syndrome and similar issues. Almost all PhD students will feel insecurity and inadequacy at some point during their PhDs (but don't expect them to show it!). Be prepared for this, when it happens!
• Generally, people are unlikely to judge a student's capability by their group. In fact, very often the best groups/supervisors do not produce the best students; the reason for this is that it's often easy for students in such groups to coast along on the backs of their supervisors and colleagues. When I think about groups I have worked in/with, they've all contained a huge range of students; some excellent, some barely passable. If you want to stand out, work hard, work independently and produce results. Be active in engaging in collaborations with other students/academics.
• Be careful about judging other student's work - that not for you to do. Be aware that differences in output are often caused by differences in aspirations and motivation that do not necessarily make a student "better" or "worse". For instance, a student that has decided they wish to leave academia for industry after graduation will have far less impetus to push out high-quality, high-impact publications than one that wants to stay in academia. This doesn't reflect their capability nor their quality as a student.