In the past Wit's End was a fairly popular item on many dps bruisers like Irelia.
This changed ever since the introduction of the Hexdrinker's upgrade Maw of Malmortius, which turned out to be superior on every dps bruiser.
At some point Wit's End got the MR reduction of Malady as a form of buff, which however barely any autoattacker does make much use of. Even magic damage attackers like Jax or Shyvana barely build it, which kind of speaks for itself. This is due to those champions still dealing a fair share of physical damage, which makes the MR reduction less usefull.
Back in the days Wit's End was more popular for far more champions than it is today as it did not have the unsatisfying MR reduction and Malmortius did not exist.
Wit's End desperately needs a form of rework. Not only, because other items are basically always superior, but also because the MR reduction is simply not a good stat in combination of Attackspeed and for the champions that theoretically want to build the item.
In my opinion it would be quite easy to fix and there would be 2 birds killed with one stone. The MR reduction does not feel satisfying on too many champions -> remove it. This removal + the item needing a buff in the first place -> buff / add stats that more champions can make more use of.
For example the Attackspeed and MR could be increased from 40 to 50. Alternatively a Ruby Crystal could be added into the recipe of the item for a 200 Health boost.
This would make the item far more satisfying to build on many champions like Irelia, Xin, Yi, etc. while not making it worse for said magic damage attackers like Jax or Shyvana due to the small buffs as a trade for the removal of the MR reduction.