Before Dark Brotherhood with every Veteran Rank you gained your pet stats also went up accordingly up to VR16, right now though their stats stop growing at level 50 regardless of your Champion Point growth so technically they are weaker by 15 levels across the board. While they applied extra stats and skill points to the lower levels, pet scaling did not get the same treatment.
Currently level 50 / 10 CP to 160+ CP:
Unstable Familiar - 16,683 health
Unstable Clannfear - 20,656 health
Twilight Matriarch - 7,945 health
Twilight Tormentor - 7,945 health
I unfortunately do not have the data on pets pre-Dark Brotherhood on hand, if anyone has definitive screenshots of their health values before DB it would be very helpful.