Well, the problem is that it's not intensity that's being varied. The things changing are metabolic pathways, movements, etc. CF would encourage you to go your hardest on all of those workouts - run your fastest 5k, PR in Fran, get your new 5RM.
I think part of the problem is that exactly what it means to "do Crossfit" is not very well defined. The fundamentals are clear - high intensity, functional exercises, constant variety - but the routines on the CF mainsite, Crossfit football, Crossfit endurance, and every individual affiliate are quite different. The mainsite does not do a good job of explaining itself, which is a well known complaint. To be fair, the info
is out there - in the FAQ, the journal, the certifications, and on the messageboard - but isn't necessarily easy to find and organize.
For example, you mentioned that CF encourages you to set a PR on every single workout. For one thing, I'm not sure that's actually CF's official stance: it may well be, but I'm not sure I've actually seen it written. High intensity is definitely a big part of CF's definition, but is it required in every single workout? Again, a better job on CF's part to define itself would help clear this up.
In practice, CF isn't much different than say, SS or SL 5x5, where you are also expected to set a new PR on every exercise in every workout. With strength training, this type of progress obviously doesn't last forever, so you eventually have to switch to intermediate programming where you attempt PR's less often. With CF, beginner gains tend to last for a *long* time due to the
huge variety of exercises, workouts, energy pathways, etc involved. I've been doing CF for 1.5 years and am still doing multiple workouts I've never seen before each week. I'm also setting PR's on most of the workouts that I do repeat. However, as you get out of beginner territory in CF with some of the modalities, you will attempt PR's for those less often. For example, I don't always go for a PR when doing squats or deadlifts. There have been discussions on the messageboards where more advanced CFers echo the same mentality: the guys with 2:xx Fran times don't go for a PR each time it comes up.
I like CF. I just don't think it's got the perfect programming.
I agree it is far from perfect. How good the programming is depends a lot on your goals. For some goals, CF is perfect; for others, it is total rubbish. This is why there are so many flavors of CF, such as CFB, CFE, etc. However, the general concepts are very sound, and CF works better than 99% of the other crap out there.
I also think it has a high incidence of injury - another cost of running at high intensities all the time.
A high incidence of injury in relation to what? Compared to a sedentary lifestyle, sure. But compared to traditional weight training, sports, jogging, and other fitness programs, it is much less clear. For example, the injury rates for sports like soccer and basketball are literally 150-2000 times higher than weight training (see the tables on
this page and
this page). Does that mean soccer is too dangerous of a sport and should be avoided?
At any rate, I don't think any official studies have been done of CF injury rates - I know the Canadian Armed Forces evaluated CF and iirc, determined it produced equal or better fitness than their normal PT, with shorter workouts and less injuries. Other than that, we only have anecdotal evidence. If you go over to CFE or even the CF mainsite and look through the comments, there are numerous posts from people coming from more "traditional" training methods (running, bodybuilding, etc) talking about how they get injured far less with CF than their original training techniques. As for me personally, I tend to get injured pretty easily in most things I do (I work hard as hell but am not too genetically gifted) and would estimate that I've had roughly as many injuries from CF as my strength training and jogging routine before it, so it seems like a draw.