Garrison has been subpar the last 150 games (last 3 years in the NHL)... before that he was a very legit top 4 dman.
Interestingly over those past 150 games... he's had fairly tough zone starts and his QoC stats have remained relatively high as well.
I'm a big believer in RelT stats as most know here... I reference them often, but it's true... they have to be used in context AND when you look back over a longer timeframe... say the last 7 years instead of a shorter time frame of just the last 150 games... Garrison's stats looks much, much better.
When you look at that larger sample size of the past 7 years... and look at all the key variables... Zonestarts, TOI, QoT, QoC, individual pts/60, RelT GA/60, RelT GF/60 and even other more esoteric stats like penalties drawn/taken, blocks, hits, takeaways/giveaway stats... I would say that overall Garrison is worth the risk of being a decent vet #7D option at the low cost of $650,000 (league minimum).
If he truly is a detriment at this point in his career... well his entire cap hit is obviously able to be buried and someone like Gravel/Jones/Lagesson likely then gets their shot at the #7 spot on the roster.