Heroes doesn't emphasize lane ganks. The most you can do is deny the opponent of EXP very briefly, considering the low respawn timers and the shared EXP from all lanes. Abathur and Murky would also not be possible if last hitting were to exist, they're characters that absolutely break the formula.
Heroes has a very specific design philosophy. It plays very differently from DOTA and LoL in many respects. There are less perceived options available due to the low level of complexity, but it can not be directly compared to other games that simply don't have the same meta game as Heroes.
This is on the level of comparing WoW Arenas to WoW Battlegrounds. The metagame is completely different, with very different goals. DOTA's progression is not the same as Heroes. In effect, you have to learn to play Heroes as its own game, not as a variation of DOTA or LoL. It has a very different meta that promotes late game team engagements and denying the opponent of the objectives. Lane ganking is not heavily emphasized, and Blizzard would need to make changes to how EXP is gained or the respawn timers to make it more effective.