While as a fellow offline solo self-found player I agree that the drop rates are comedically low and not balanced with SSF in mind, it is absolutely possible to beat Hell with basically every build without best-in-slot gear. You may not be able to efficiently farm a lot of areas in the endgame, but you can at least beat it.
You just have to grind more. Your level matters a lot, especially for melee. For casters, +skills are massive increases in power. Leveling up and farming for a long time in Nightmare is totally standard before entering Hell, if you’re playing solo.
Farm NM bosses and get the Vipermagi, Gore Riders, Gface, Spirit weapon, Wizspike, Insight, Tal’s mask, etc. That will boost you and your mercenary’s power. You won’t be able to get a lot of things that many online players take for granted (HOTO, CTA, Enigma, Grief, Fortitude, Infinity, Eth Reaper’s Toll, Andy’s helm, etc.) but you will get enough to proceed. It won’t be fast, it won’t be easy, but it’s absolutely doable.
Later on, find a Hell area you can farm half-decently and upgrade with the slightly more accessible runewords for you and your merc, like Oath, Pride, or Treachery. Grab that Monarch for Spirit shield, stack some IAS or FCR (depending on your build), find a Shako. Maybe luck into a good +2 skills rare amulet or even Mars’s.
It’s not extreme endgame gear, but it’s enough to get somewhere.
You will probably still hit a wall at some point. Eventually you get to a point where you need to farm super efficiently to have a decent chance of getting the true endgame gear… but you need the true endgame gear to farm super efficiently. That’s the wall I’m banging my head against at the moment. Hundreds of hours into D2R with no high rune drops (so no Infinity, no Grief, no Fortitude), no Arach’s, no Griffons, just a few low-rolled facets with nothing to put them into, barely any useful Skillers, etc.
It can be frustrating, because the RNG is so intense. In some cases a single Lo rune can be the difference between painfully slogging your way through p1 and dying all the time versus efficiently clearing p3+ areas. An inventory of skillers can triple your damage. Enigma is absolutely broken. D2’s power curve gets pretty screwy at the high end!
So yeah, I can’t tell you everything will go smoothly, and I certainly won’t call you a whiny baby like a lot of people on this forum will. I really understand your struggle. But you do need to put in the work in Nightmare, as much as you can, before making the leap to Hell. It’s just that kind of game.