in galios case.... he only builds
which is great on him. but anything else MR related is garbo
(used to be alright with 20% cdr, now its just not)
grail doesn't give enough ap, and why build it when you can solve all your mana problems with
instead?
used to give 35 and be a strong lane tool, now it doesn't provide all that much damage reduction anymore because of thunderlords/dft adding so much passive damage.
oh look, theres all the items a mid laner would even consider buying, 3 of which are trash (BoC, grail, merc treds) leaving just spirit visage, but the MR -> AP bonus just isn't enough to justify it when you could build raw ap/health instead. your W already heals you based off your AP, and it gives enough MR when active to still function as a tank.
any item with MR on it.... is not worth building on a mid laner under any circumstances at this time. (outside of abyssal, banshees, spirit visage, and guardian angel) but if you build those items you deal dirt for damage and your utility is non existent.