4) Havok’s Death
You know mutants are going to die in an X-Men movie subtitled Apocalypse. And they do, just not in ways you expect. Alex Summers, aka Havok, aka he with the similarly-aged parents, is a fairly expendable character not seen since First Class bar a minor cameo, so it makes sense that Singer would choose to waste him as a way of highlighting the threat of Apocalypse and his Horsemen.
What makes less sense is that Singer kills Havok off-screen, and during Quicksilver’s upbeat, musical rescue sequence no less. Tonally the whole thing feels off, while treating Alex Summers’ death as an afterthought when his brother Scott is a new, integral part of the cast doesn’t ring true. It feels like Singer and the writers are clearing house of a not particularly well-loved character, without putting any effort into disguising the fact.