The HW title has been like Cain v JDS, Cain v Bigfoot, Cain v JDS, Cain v Bigfoot, Cain v JDS, DC v Stipe, DC v Stipe, DC v Stipe for the last decade, with a few token sacrifices thrown in their. That's a bit of an exaggeration but the match making for the HW title has been atrocious for a long time. Stop it.
Cain and Bigfoot only ever fought for the title once, their other fight was not a title bout.
Cain/JDS; a worthy title fight.
JDS/Mir; Overeem popped for steroids.
JDS/Cain 2; Cain finished Silva and there was no one else.
Cain/Silva 2; Silva finished Browne and Overeem to get a title shot.
Cain/JDS 3; JDS had finished Hunt, the UFC didn't have anyone else at the time, and "trilogy".
Werdum/Hunt; Velasquez got injured.
Werdum/Cain; Velasquez wasn't injured.
Werdum/Miocic; Miocic finished Hunt and Arlovski.
Miocic/Overeem; Overeem finished Struve, Nelson, JDS, and Arlovski.
Miocic/JDS; JDS defeated Rothwell, had a win over Miocic, and there wasn't anyone else.
Miocic/Ngannou; Ngannou had wins over Arlovski and Overeem.
Miocic/Cormier; Cormier was the LHW champion and previous Heavyweight contender.
Cormier/Lewis; Lewis defeated Ngannou and Volkov, and the UFC needed a headliner for the MSG card.
Cormier/Miocic 2; Lesnar pulled out, Ngannou hadn't done enough to earn a title shot, and there was no one else.
TLDR: Most of your complaints have to do with injuries, PEDs, and a lack of depth rather than the UFC's matchmaking.