Well you do have blanket immunity if you have a good and proper chem seal.
If your armor jacket has 6 levels of chemical protection, it's STILL an armor jacket. Ok your chest and arms are very well protected, but your hands/face/legs/feet are completely exposed still. I can see an argument on the flipside that you shouldn't even get those dice
It's abstract... I think it works mostly well as-is. (what DOESN'T work is gas masks... 100% effective vs inhalation means 0% effective vs toxins that are both inhalation AND contact...)
SSDR, I want to understand what you are saying, so I will ask you two specific questions.
Is it reasonable that any Body+Willpower total of less than 11 cannot even possibly resist the effects of a cloud of Pepper Punch? (I guess barring dropping lots and lots of Edge)
Is it reasonable that a rating 6 chemsuit (not an armored jacket mind you, but a purpose built device to protect you from things like gases and toxins) provides me with much less than 10% chance of actually avoiding being affected by a cloud of Pepper Punch?
If both are yes...fair enough. I see no reason to argue with you, we just have very different perspectives on it.
Well... "is it reasonable" is an opinion question.
But my opinion on #1) is that I'm generally ok with the status quo. If a substance is known to have some effect in some dose then that should be the result, rather than letting the dice say what happens. For example, so many grams of cyanide is lethal. If you're exposed, you should die. You shouldn't roll to see if you die. Of course, in a RPG there's an expectation for hero armor, so I'm also fine with a "lethal" dose of a toxin proving to be less than lethal because you rolled really well. So that's the status quo: barring edge, yeah you're probably gonna suffer the effects of whatever the toxin does if you're exposed to it. Seems right and natural to me. Now, I do have a minor quibble with the premise of your question. If you're building a "tough" character who is meant to resist toxin attacks, then you're very much doing it wrong if you're not using augmentations and/or gear. So the "you can't reasonably resist a toxin by only rolling body + willpower" point is imo flawed. If you're trying to resist them, then you'll be rolling more than just body + willpower. Which segues into:
#2) Is the question of the efficacy (or lack thereof) of those bonuses. A couple of dice here and a couple of dice there may not look like much, but add them all up and you've got a respectable dice pool. 6 dice from chemical protection, 6 dice from nephritic screen, maybe a circumstantial edge because you have some goggles on or a scarf covering your nose and mouth, and we've got a much stronger situation than "naked" body + willpower, no matter what those values might be. Also note that statuses have a duration at the GM's discretion. If you reduced the CS/Tear Gas to power 1 and therefore you still suffer the Dazed and Nauseated statuses because you didn't knock it all the way down to 0, the GM should probably be saying your statuses wear off faster than the guy who got few or no hits.
So, for those reasons, plus the existence of Antidote patches, I'm fine with toxins being the way they are. Yes in my subjective opinion I think they're "reasonable". Are they disproportionately powerful compared to options like guns? Also yes. I'm in no way a fan of the idea of coating your katana with narcoject so that your weapon DV is irrelevant and the toxin takes your victim out. But stacking two DVs into one attack is a different ball of worms.
I lied, I am going to try to convince you for a moment. 
Lol, ok

The issue here is not that things like chemical protection on armor, chemsuits and respirators are not 100% effective. That makes perfect sense. As you say, they don't have chem seals, independent air supplies etc. But that potential ineffectiveness is already represented by the fact that they add dice to the toxin resistance test instead of providing immunity (as hazmat suits and gasmasks do).
Therefore the issue is that because the power levels of the toxins are off the charts, even at their highest ratings these devices are still practically useless, certainly providing far less protection than a simple reading of their descriptions implies. Like, if the description of chemsuit added "btw, even in a best case scenario you will only get less than 10% chance to resist common off-the-shelf crowd control agents like Pepper Punch" I think you wouldn't even think of paying the price for them.
Way I see it is if you have some kind of armor that is all-encompassing, you'll just get the chem seal option rather than the inferior chemical protection option. If chem seal is not an option because the armor is not all encompassing, I'm fine with the chemical protection being far from immunity when it's on armor that leaves your face/large portions of your body exposed. As I said before, it's almost silly to say it helps in any way whatsoever, really.
You'd just accept you are going to be Blinded, Nauseated, Dazed, and Stunned if someone uses them against you and move on.
As an aside, not only are there antidote patches (if you're fast enough with the slap patch before the statuses take effect), see also the fancy gear called "Liter of Milk" on pg. 157, No Future
