Meh. Let's maybe focus on the plenty of actually heinous stuff Putin has done (and continues to do) instead of psychoanalyzing and vilifying a slightly eccentric fashion choice?
I wear heels daily (because I like them and find them comfortable - no problems with my height with or without them), and I strongly doubt that that's going to turn me into a tyrannical world leader any time soon.
If they do it in private, then yes you might call it a lame insecurity.
If they do it only at public events where they're constantly being photographed in groups of people, it's smart image control. A leader is a symbol, and different height differences project different messages visually. That doesn't mean you need to be the tallest, but being the shortest in every photo may give voters a perception that works against you. It's not vanity; it's reality.
Actors stand on apple boxes all the time in film and TV shows, because the director wants a specific height difference between characters to arrange a shot just right, that isn't the actual actors' height difference. Not lame insecurity -- it's producing the image that communicates what you want.
It works for actors because the director controls the camera, but for a politician, it has the opposite effect (at least in a democracy, russian politics isn't too far from a TV show anyway).
Sarkozy was mocked all the time for being short and insecure about it, nobody ever noticed that François Hollande was small until they appeared together after Hollande's election: he was in fact smaller than Sarkozy but nobody had ever noticed that before.
Counterpoint: Zelenski is a short guy and I don't think it hurts his image. He comes off as something of a bulldog. The fact that he's fit helps a lot mostly he's good at using what he has and crafting an image off of that, rather than trying to fake something.
The high heels haven't hurt Putin politically since he's a dictator but it's ruined the careers of other politicians like Ron DeSantis.
Thank you for mentioning DeSantis. It helps that Zelenski also built an image of being a battle-hardened soldier.
When Zelenski was criticized by a reporter during the meeting with Trump for not wearing a suit, his comeback was that he'll go back to wearing suits ("costumes" though I hear that may have been a mistranslation on his part) when the war is over. The reporter was trying to frame his attire as disrespectful to the President, Zelenski's response made it clear that he'd have found wearing a suit disrespectful to his people who don't have the luxury of returning to civil life until the war ends. Make of that what you will but it signalled confidence and empathy. It came off as authentic. Trying to compensate his height with footwear would have had the opposite effect and conflicted with this.
DeSantis on the other hand tried to appear "tough" and decisive but was ridiculed for his footwear because it was so obvious and so exaggerated that it made him appear extremely insecure about his height. But I think it would have looked even worse if he had been in Zelenski's position (and wearing a uniform) because of this contradiction.
https://www.youtube.com/watch?v=lY6lHjZjYXE