Complex sentence: One notable deficiency of the HP-25/25C was the lack of a subroutine capability, at a time when the TI-58 and even the earlier SR-56 had subroutines.
Split into simpler sentences: One notable deficiency of the HP-25/25C was the lack of a subroutine capability. The competing TI-58 and even the earlier SR-56 had subroutines.