Problem with the +0.3 seconds flat CC increase is that:
A) Knockups are generally coded as a stun+a dash. In effect, it would increase the stun time attached (also, you can qss the stun and then use a dash to get rid of the knockup.)
I was not aware of that, if that's the case then I can see the issue. However, it's really something Riot should fix anyway.
B) It would be incredibly OP in most situations: rammus taunt goes up from 1.25/1.5/1.75/2/2.25 to 1.55-2.55 seconds. At level 1, that's a ~30% increase, and a ~15% increase at max level. Sejuani's Ult goes up from 1.75 seconds at max level to 2.05 seconds- that's a 15% increase in effectiveness. Since most CC is less than 3 seconds, they'll all have an increase in effectiveness >10%. Do any other quints increase anything's effectiveness by >10% at all stages of the game? Didn't think so.
tl;dr- they'd either be a must-have for champs with CC or they'd be useless.
I see where you're coming from here, but I'd have to disagree. While it would increase the length of CC noticeably throughout the game, it's nothing like tenacity does to CC in the opposite direction. These runes would be very easily countered by any form of tenacity, and likewise these runes would be a counter to tenacity itself (something LoL is lacking completely btw). Now these runes wouldn't be without consequence, if you take all three Quints you would lose out on a large amount of stats for your early game. They would be designed so that champions like Veigar who need their CC to stay alive/land effective combos wouldn't get screwed over completely by someone else buying tenacity boots.
You also seem new. -time dead is a horrible thing to even put in runes, because it only comes into effect if you screw up and die- it doesn't actually help you win games, it just helps to maybe stall it a little longer/helps you feed more. The -time dead quints should be removed.
I've actually been here for several years... and while I recognize that spells like Revive and the -time dead runes CAN be used by intentional feeders, taking them doesn't mean you're going to die all the time just like not taking them doesn't mean you'll never die. In short, you shouldn't take -time dead runes if you PLAN on dying, but they can save you precious seconds on your respawn timer and you should know that in 19/20 of your games you're going to die anyway. If you're in a situation where you know you're going to be dying, -time dead can be very valuable. It's better to be able to defend your nexus at all than to have a few more stats but not be up in time to use any of them.
Tenacity is relatively common, in that it's on merc treads for any tanks and on Zephyr if you're adc and need it. If you really need it, it's on one of the elixirs too.
But what if you need tenacity, but can't spare the item slot? What if you don't want to drop 400 gold into it every few minutes or you need another elixir? I'm just saying it would open up more playstyles and strategies.
And the %damage to/from monsters wouldn't do what you think they'd do. Yeah, others could possibly be made viable from them, but ones that already excel would just get better. I.E. if they increase damage by 10% total, that's taking a 2 minute clear down to 1:50 (because some will be lost due to damage inefficiency). It'd just be another gate to the jungle, which is pretty difficult to just pick up anyways, especially with the new harder jungle. We don't need any more gates there- if you wanted to play ranked, your team may very well flame you or troll because you're not using the most efficient things in the jungle. On the flip side, they might end up worse than any other runes, in which case there's no reason to buy them ever. It's one of those things that it'll either be OP or useless due to how it's set up (Like Poppy).
Certain junglers Lee Sin need to be nerfed anyway. I'm not saying they should balance any champion around certain runes, that would be awful. But saying that +%damage to monsters runes shouldn't exist because someone would benefit more than others is like saying that there shouldn't be AS runes because Udyr and Vayne benefit from them more than Sejuani and Corki. It's not like they could take the %damage to monsters on top of the runes they already have.
And don't dis my Poppy girl, she'll ult your support and dive your carry and bruiser without taking 100 damage.
Seriously though, thanks for taking the time to respond to this. Nothing irks me more that when someone says "no" and doesn't give a clue as to why.