(semi-newbie) Is the last mission of the main quest meant to be so damn frustrating to play solo?

I used to play a little bit (I got to like level 60) around 2 years ago and I had a lot of fun, but I ended up quitting because I lost all of resources trying to launch a nuke for the last mission. Around a week ago I decide to reinstall it to give it another try, so I stock up on ammo and good weapons, refine my build, play the quests to become a ghoul (so radiation isn't a problem anymore) and get ready to assault on the launch sites (making sure that there's no cooldown).

The robots are tough and they are so many that my laser rifle and laser minigun (which were in perfect conditions when I entered) end up breaking, but I still have some other decent weapons so for the first time I finally manage to get close to the last section. I fix the mainframe, the door opens but when I turn left the silo door to access the last section is still closed. I looked up some gameplays and guides and everyone it shows the silo door automatically open when the mainframe is fixed. I end up dying right in front of it and get kicked out of the launch site.

Long story short, after 2 hours I have lost almost all of my ammo, my junk and my decent weapons are all broken. I was looking forward to finally complete the game but I'm very tempted to abandon it again. Is grinding all over again my only option? Is it feasible to do solo without super high-end gear and min-maxed build? What the hell is up with the silo door?