Okay first of you are heavily over generalizing things, so you lost my belief that it might be more then you just salty because you can't use the same champion the same way all the time and win like you use too. Its called adaptation.
To directly address your "points" that you brought, i provide counter point.
Your first point has some merit, but you are taking it out of context and aren't addressing all the points. Some champs are literally designed immobile because of their power budget, take the fairly recent champ Vel Koz for example, he is crazy strong when you and your team play to his strengths, but struggles if you let them get in his face. Other champs are designed with mobility in mind and they try to adjust the power budget in mind with that, unfortunately it is fairly hard to quantify exactly how strong mobility itself so that they don't have too much damage or don't have enough damage where they aren't even a threat. Also Riot has already address the "mobility creep" argument and they stated they actually have plans for champs with out a lot of mobility.
With your second point, your entire argument is utter garbage. You are comparing champs that fulfill different roles or who don't even do the same things. Tyrn is a melee adc who excels at dueling and split pushing, his ult only prevents him from dying for a short time. It doesn't not give him health back and because of the nature of him it doesn't guarantee survival. Kindred on the other hand is a marksmen who excels at teamfighting and champion killing, who ult also affects everyone in the radius preventing them from dropping below a certain health and healing those still inside when the effect ends. Unlike with tryn, kindreds ult can kill your entire team and cause you to lose a fight you would have won, whereas with tryn its only him if he messes up. Vayne and poppy aren't even related at all, besides poppy's rework is up soon anyways. Thresh and Janna cannot be compared because they do different things. Janna is the ultimate disengage support, Thresh is more of all rounder, he can disengage, engage, and harrass. With Skarner and Warwick they fulfill different niches so thats not a good comparison, and if its just the ult you are talking about why aren't you including Malzahar. Volibear and Rammus, i got nothing because i can't even see what you are trying to say about them being the same.
Your complaints about the juggernaut items are wrong. That's not why they were changed and they certainly weren't "nerfed like a motherfucker" they were changed to give diversity in the tank role and because a couple of them were way too gold efficient. Some of them were nerfs, just so they could address the efficiency issues, while others were changes to their role to give better diversity.
Also, its not a buff to Marksmen, so much as its an update to items and a pass over the champions to give better build diversity and Champion pick diversity by better defining their niches.