Magrit is a bitch of a boss if you try to face him straight, but I don't think he's exactly what you describe there, particularly in regards to patterns. There are some patterns, but part of why he's so difficult is the way he so fluidly shifts in and out of patterns, countering the player in a very natural way, thus making it feel more like a real fight than a lot of past Fromsoft bosses. It's actually really good, and adds another layer of challenge. I think the thing that myself and a lot of veteran players forgot was some of the tools we were taught several hours before. Ashes of War and counters are much more important than they initially seem.
And then of course there is the mounted strategy that
Thac0 mentioned earlier in the thread, which hadn't even crossed my mind. That apparently makes the fight much easier, which makes perfect sense because it tends to defang intense combos that enemies can pull off if you're moving at foot speed. Not sure if I like that or will utilize such tactics for unmounted humanoid enemies myself, but something to keep in mind the next time you meet an extremely difficult enemy with a suite of nearly unforgeable combos and counters.