Firstly, Scout can be a useless hero cause most players sit there and watch your team die then try and go for the kill steal and either die brutally or run away which results in rax. My favourite hero was predator before his ulti got heavily nerfed and become more useless for armour reducing then any other hero ie. pestilence, soul stealer, demented sharman.
Secondly, as mentioned your team can choose such a flawless combo that synchronising their ultis together will result in genocide everytime unless your team is retarted and unfortunately it is in most cases unless your playing with friends. I remember almost getting annihilation with soul stealer's ulti activating assassins shroud on seeing as the opposing team had 4 intel lol.
Lastly, Rampage just takes some time to use to and can be potentially the carrier of your team if you know how to coordinatie ganks with your charge at heroes that are alone. That combined with hack and slash and elder parasite your one tough hero.