Yes, I should not have said "impossible": nothing is ever impossible to breach. All you can donis to make a breach more expensive to accomplish.
Those separate tpm chips are getting rare... most of the time they are build into the CPU (or firmware) nowadays. That makes sniffing harder, but probably opens other attack vectors.
Anyway: Using a TPM chip makes it more expensive to extract your keys than not using such a chip. So yoj win by using one.