It was around the Imperial City dlc that I noticed stam and magic getting out of whack with one another, and also when significant class imbalance issues seemed chronic. I'm not sure it was this patch precisely that caused it...it might be that this was the timeframe where the player base began adapting to exploit game changes in a way that resulted in imbalance. Several things began occurring:

1. The CP system allows a character to overcome weaknesses. Some classes benefit more than others. For example, magsorcs were designed with powerful damage abilities offset by their high cost. Stamblades are squishy. Through the cp system, a stamblade can get like 40% less squishy through hardy and elemental defender. But a sorc with unlimited magic used toward shields and heals can become 300% less squishy.

2. The game began expanding the number of available sets dramatically. More sets allow players to exacerbate the power creep strategically. Stamblades have been able to stack sets with ridiculous dps procs, making them deadly in pvp. And magsorcs could stack sets that return magic, allowing them to spam their most expensive skills continuously.

3. The designers (imo) began obnoxiously favoring magic, lol. There's no one CP or set that makes magic builds superior, but there are a lot of little things that add up. For example, Arcane Well returns magic. A little...but even a little helps. Then they offer a shield that offers a little magic on damage. Etc, etc, etc. Back in vanilla, my magsorc and magplar would run dry a lot. They haven't in months. I would kill for a shield on my stamblade that offered a 9000 damage shield for six seconds with stam returned with every hit.

4. After IC, the killer meta ability became standard. What I mean is that there was perpetually one spam ability that became utterly obnoxious and OP. It was wrecking blow for a while. Then snipe for a bit. Then radient destruction.

Whatever caused it, for over a year the best players have complained that stamina builds are not competitive in end game PVE. And players have complained about magblades for quite a while. I don't know...I read these forums all the time...and my experience is that every major update, zos comes up with a bunch of "imperatives" that no one asked for, while ignoring popular requests. As an example, I never recall reading much about people wanting major frost staff changes...but ,agblade players have asked for some magblade abilities to be looked at. So when the last patch came along, it was weird that we got all this frost staff crap and no attention to the stuff the community was asking for.

But...meh...it's still a great game, and the fact that the dev team seems (I'm sorry) either incompetent or too arrogant to listen has continued to produce a wildly fluctuating, unpredictable product. And so perhaps that helps make ESO a little more like real life, where part of the challenge stems from things not being fair or balanced, and never quite knowing of things are going to work as they should.