I can't speak to Timbers because it's been a while since I've seen something he directed.
As for Sam Gold - If you look back at his credits, he's always been pretty hit or miss. Not only that, but he's employed a wide range of styles over the years, ranging from hyper-naturalism to safe-and-normal to bizarre experimentalism. I don't think anything has changed much in the quality of his work over time, as he's been so inconsistent for years.
Ivo Van Hove is the exact opposite of that - he pretty much always does the same few things. He's not overused, he's just over-exposed. The more people see his work, the more they realize that he's constantly pulling from the same bag of tricks. Lots of people are praising the staging of Network who have never seen a Van Hove show before - I particularly hear people mention things like the fact that they have a live-feed scene outside the theatre, but that's the THIRD time I've seen Van Hove do that, and I bet he's done it other times. Having said all that, I'll still keep going to see his shows because it's interesting to see how different material works with the "Ivo-treatment." I also think Van Hove does better work when he's directing an existing piece of theatre written for the stage (View From the Bridge, Crucible, etc.), as opposed to his film/book adaptations (The Damned, Obsession, The Fountainhead, etc.)
When I saw this thread title I actually thought it would be about something different. I don't want to hijack the thread too much (in fact maybe this topic deserves its own thread), but has anyone else noticed that there's always 1 or 2 directors per season who end up directing 3-5 shows in a short period of time? Last year it was Lila Neugebauer, the year before it was Sam Gold, this year I feel like it's Leigh Silverman. It's an interesting trend!