Performance Condition

Performance condition during the run shows current deviation from last VO2max estimate. So +2 and -2 from similar runs are to be expected if the VO2max before the run was different (including decimals, which the watch doesn't show). And the value at the end of run is not important, it's the whole progression of the performance condition during the activity. The whole graph is used (after filtering) to estimate if the VO2max has changed and how much.

It does take hills into account.

Yes I agree with everything you say about what it’s supposed to do but in my opinion it doesn’t. 

When you say it doesn't do what it's supposed to, are you trying to the performance condition or also VO2max?

I mean the performance condition is supposed to tell you how easy or hard the run was compared to your fitness but it’s not very good at doing that. 
As I said I think it is not fit for purpose, people can agree with me or not but that is my opinion. 

I think that point here is that performance condition tends to be correlated with changes in Garmin’s estimated VO2 Max, since it’s literally defined as the percentage difference between the VO2 Max estimated for the current run, and your estimated VO2 Max before the run. So if you’re unhappy with performance condition, you might also be unhappy with estimated VO2 Max. For example, if I run 10k with my performance condition around +5 for most of the run, it’s pretty likely that my estimated VO2 Max will increase (even if the increase is small enough that the rounded number doesn’t change.) 

I know it’s probably not what you’re asking for, but performance condition alerts can be disabled, and you can ignore the graph in Connect, so it’s the closest you can get to Garmin removing the feature. But ofc it will still internally correlate with changes in estimated VO2 Max.)

“Also doesn’t work for intervals as it only track average speed and heart rate”

Are you sure about that? I’ve had a positive performance condition (around +4/+5) when doing intervals, despite the fact that my average pace (which includes rest) might be slow compared to steady state runs. If performance condition only ever took average pace into account, I might expect most or all of my interval workouts to have negative performance condition, considering I always record the rest intervals.

The performance condition is not meant to tell you "how easy or hard the run was". A performance condition number only tells about your performance at that specific point in time, that's why you have the whole graph. That's also why it cannot use the average pace. So the performance condition at the end of a run only tells you about your performance... at the end of the run, not about the whole run. Looking at the whole graph might tell you something about when fatigue starts to kick in, if you know how to interpret it.

This is why I personally never look at the performance condition numbers afterwards. They are sometimes useful during the run. For example if I've done 2/3 of my planned run and my performance condition is -7, it might be a good idea to listen to my body and ask if I should cut my run short and not continue the full remaining 1/3, of course depending on what the goal of the run was. And if I feel a little stiff at the beginning, but the alert gives +6 as my performance condition, then it's probably just lack of proper warmup and will pass. But if it was -4, I might consider taking it easy.

Ok, no problem. But just out of curiosity and related to what FlowState wrote, are you still happy with your VO2max? (Because it's based on the same data as performance condition).