I agree, however, the item is a blessing and a curse in some situations, which is why it's a situational item for most.
For example, If you Zhonya (stasis) while running to dodge a Veigar ultimate, he is almost guaranteed to E stun you and burst you down with a W+Q
However, if you are in a smaller skirmish or are engaging into a team, being put in stasis would, in some cases, be understandably thought of as overpowered, but that would make the skirmish or teamfight a number advantage for the enemy team, even if for 2.5 seconds, which is a very long time for you to lose a fight, especially if you are carrying a team.
However, the build path for Zhonya's Hourglass is a very good one, if not the best in the game. With the buildpath being:
1 .Armor + AP that increases from minion kills,
2. AP + CDR,
3. and a free stasis before you even finish the item.
Which is a huge reason why I agree with you.
Take away the armor or some of the AP, and you have a very good situational item, lower gold value combined + a high cooldown with a good active makes a decent item, but as-is, i'd agree with you and say it's slightly overloaded, though the champions I play rarely have a hard time against people who build Zhonya's Hourglass as an essential item.
The Stopwatch rune is really only good around 12m though, and it can be the reason some champions like Renekton or Jax can all-in dive you under tower with a minion wave shoved in and press a key and make what would've been a 1-1 a free kill, so I see why you'd be slightly tilted from experiencing something such as that.