Potion charges are a gimmick that doesnt make the game harder

The flask system is a way to balance utility vs restoration potions. The flask system is ALSO a way to balance potions without a stupid cooldown mechanic.

They're also permanent items. Flasks, being subject to modification/upgrade, are as much a part of your build as anything else you can name. Drink-and-discard potions are precisely that: disposable and far less integrated into your playstyle.

Flasks also have far more utility than merely healing, as any advanced player will tell you. It's easy to allow yourself to view them merely as healing/mana, but look at the builds of the week and tell me how many use only basic healing/mana flasks.

Also, given said mods, you can recharge flasks due to certain conditions. Surgeon's prefix, for example: every time you crit, you get a charge. This can mean the difference between life and death.

Finally, tpapp is dead right, if I'm reading him correctly: if you are diligent in keeping your flasks up-to-date via baubles and orbs, the game is MUCH easier. You really don't have to, but understanding the difference between a basic healing flask and, say, a bubbling healing flask of heat can again create large gaps between a new player and one that wins races.

I like garr0t's idea, and I think I've mentioned before either here or in-game that an 'iron man' mode wherein returning to town won't restore flasks is definitely something I'd like to see.

Flasks and charges are a gimmick only if you don't really consider what they represent and how to use them well in your build. This appears to be the case here.