In a Pathfinder surprise round, characters can do only one "thing." Translated to 5e terms, each character that acts in the surprise round could take one of: an action OR move OR a bonus action. And that action could only be used for a single attack even if you have Extra Attack.
It lessens the potential for absolutely nuking the enemy during a surprise round, while still allowing a surprise round to be impactful.
That sounds almost exactly how my 5e sessions play out. Not sure if that is core rules but it makes sense to us. You stealthily move into position which is free movement, not part of a round. Everyone attacks at the same time, then initiative starts. Doesn't matter if you have multiple actions that can be done in a turn, you only get one for surprise because the enemy obviously knows you are there at that point.
As it stands with the right build and enough patience you should be able to beat this game without ever even taking damage.
The sad part is you can do it with any build because of all the cheese.
