It seems to me that you're just handwaving the whole squishiness issue away by declaring that "monks are fine 'coz they get Stunning Hand at level 5". It's not a good argument. To reach level 5, monks have to survive the levels which precede it, and they are quite weak at those levels thanks to rogue AC, rogue HP, melee-oriented class abilities, and no consistent way to dart in and out of combat. If you were to preface your argument with "I played a monk from levels 1 through X, and I generally had no problems surviving because of Y", then your comments would be more helpful.
Right. Let's look at why you think they're weak and examine if that's real or not...
Rogues can have AC 12(Studded Leather)+Dex(15), Monks get AC 16. The only way to get an AC 16 at the start with Point Buy is to be a Monk, a very strange Barbarian, accept Disadvantage on Stealth, or accept that you're doing less damage with a Shield. Yes, sometimes you're going to get hit because the monsters roll well. Sometimes you're going to get hit because you didn't play a Monk and did less damage than one, so the monster didn't die.
HP. Monk has no real reason to invest in Str, Int, or Cha. So getting a 14 Con is easy to do. That's not true for Rogues, who have Int/Cha tasks typically.
Melee-focused abilities. Tons of other classes are melee focused. Not a big deal. And as I noted, the Monk can throw a javelin and still get off their bonus action attacks. Wait to see if you hit the target and if you do, go in and kill it with your martial arts swing.
No reliable way of darting in and out of combat. Monks are one of the best damage dealers at low level because they do 1d8+3/1d4+3 or an average of 13 damage. That jumps up to 18.5 if they do a Flurry of Blows - and if your DM is playing Short Rests correctly, that's every combat usually by 2nd level. Barbarian not doing a Rage? 10 damage. 7.5 if using a Shield. Rogue? 1d6+3+1d6+1d6 or 13.5. If they have a friend already next to the target. Note how the default Monk does significantly more damage than either of them with the same to-hit chance - enough damage in fact that they have a decent chance of killing their target.
And this is besides the point - you don't generally want to dart in and out of combat in 5e, because in doing so, you're freeing up that target to go unimpeded towards the weakest member of your party. Say the Wizard or Sorcerer. It is almost certainly a net-win if the monsters spend a lot of effort attacking the PC who has already gone rather than the PCs who have yet to go. As the party Monk, you might not appreciate it that your DM is focus firing you, but that's the correct action to do if your DM then spends all his effort going after the wrong target.