On a map like Shoreline where running even one second late off the spawn could be the difference between getting a ledx or not, spawning on the tunnel side makes it so that 9 times out of 10 you can't even contest the popular rooms.
I have religiously ran Shoreline over the past month and I know the optimal and most efficient path to west 301, east 226, and tape key room from all spawns on the map. If you spawn on the tunnel side, you just have more shit to deal with before even breaching the resort area. The swamps, navigating the cottages area, potential Saniturd, open fields surrounded by other PMC spawns, and the fact that tunnel is much further away from resort then road to customs is. All of these things actively delay you from getting to resort and even being able to engage in a gunfight to stop someone else from getting the ledx. None of these delays or obstacles exist on the road to customs side
I have found that if you spawn tunnel side as close as possible to resort (just below bus station), you still can't even lube yourself up and get to west 301 before an efficient pather from the furthest road to customs side has already hit tape and 226 and is unlocking 301. Forget about rubbing yourself down if you get a cottage spawn but you better hope Saniturd doesn't black your leg from 300m out through 10 bushes as you're trying to get to resort. The only way is if you get lucky and there is an early PMC gunfight between the west and north road to customs spawns or Saniturd is in resort delaying their push and you hoof it across sky.
Thanks for reading my rant