It is possible to pounce and/or barb outside in karith (I've done it sometimes), but extremely super difficult, and fair to say improbably. With multiple jet campers outside, it become even more improbable (approaching virtually impossible).
Yes, jet camping can be much more of an issue on Karith than on atcs. But the thing about jet camping away from your base and the enemy base,that takes them away from both defence and attacking, so you can generally ignore them. If, however, humans manage to build outside, then that becomes a very difficult scenario, however the buildables are still easier to take out than the jet campers.
Something else to consider is how different game play makes problems/annoyances on various maps non-issues. For example, jet fuel and/or a flying alien can eliminate the issue of jet camping.
I never really considered the vents in Karith to be a big deal. Just get some poison, and flank at the right times.
Regarding parts of maps restricting/eliminating viability of certain classes in general, imo that adds to the strategy where some classes become more useful than others. The it is more about figuring out the right tool for the job rather than always throwing a sledgehammer along with the whole toolbox at the job.