I can't say for definite that your recorder is fine, but I suspect so. In the past I have played recorders and found that it is definitely hard to play loudly on alto and tenor recorders, especially in the bottom half of the ranges of these instruments. I found the problem is worse with the tenor than with the alto, and it might well be because of these problems that the recorder started to fall out of favour with composers, who started to include "newer" and louder instruments like oboe, cor anglais and clarinet.
With careful practice, you should be able to judge more accurately exactly how hard you can blow before the note "breaks" and then you can get a reasonable degree of variation in volume, but it will always be limited compared to the other woodwind instruments, I'm afraid.
One solution is to make music with other recorder players - they have the same problems, and there is a lot of good music for recorder consorts of various types.