The real reason the source engine had to be scrapped and you will not believe what I am telling you.
It was slow on purpose to combat RMT. SE in those days were coming from ffxi rmt hell and wanted to do something about it. Anyone remember moving items from inventory to retainer? Took a minute or longer just to move one item. They had that game built from the ground up to be slower and less responsive. The combat wasn't that bad it was quite good and fast paced. I ran the game with max settings at a very good frame rate. Even with one character on the screen some parts would slow down so it wasn't all because of the max of 30 or 40 on one screen. Think about RMT and you think real hard about how bad things have been. You will get what I am saying eventually. Security can really slow stuff down. Antivirus on and email server anyone? lol you see my point.