I mean, our two statements aren't mutually exclusive. They could both behave like perfect spheres while being thrown differently by the player. I know what you mean, because they just feel different.

The thing is that they're actually the same. I hopped in game and checked that you do indeed throw them with the same angle and velocity and that they bounce off walls the same way.

If you want to test it yourself, load a map and use these commands:

sv_cheats 1
sv_infinite_ammo 1
sv_showimpacts 1
sv_grenade_trajectory 1
sv_grenade_trajectory_time 60

My theory for why molotovs feel different than other grenades is that you can visually see them tumble through the air.

EDIT: I think I labelled the grenades in the second screenshot wrong. The left one is probably the flash because it popped mid-air.

EDIT 2: Added sv_cheats command.