There is "gear up" and there is "gear up" though. If your goal was to go full Tals or IK that's doable, the chest pieces are very rare but in trade value they were around Ist/Gul/Vex when I played regularly, and sure if you wanted to just make a Hoto that was doable too, maybe Call to Arms/Chaos. But if you wanted Enigma, Chains of Honor, Beast, Breath of the Dying, Doom or later Grief + the mercenary polearms, the high quality charms, Stone of Jordan, high quality rare rings and skill/ED circlets, ED jewels etc you're talking a ridiculous amount of extremely rare once in a lifetime drops.
Lets say you're boosting a player for the Hellforge that's approx 2000-3000 boosts to upgrade to a Zod, that is running a new char through act 1-5 in normal, nightmare and then Hell act 4 for the possibility of getting a good rune drop, maybe you hit the jackpot and get an Um (NM) and a Gul (Hell) once in a blue moon but most of the time getting an Um from Hell is pretty good luck, that time investment from 2 players is massive, it's more than most players would play during a ladder season and that's just one task.
Or you could go to a trade game or D2jsp, and you were absolutely dealing with duped items and buying from people botting several accounts, but that's the only way to beat the extreme rarity if you wanted to actually have a really well geared char in D2. Some builds required less gear than others, but I don't think I ever met a player in the years I played D2 in 2002-2007 and on and off since who legit geared their chars to properly high gear level, I'd give props to anyone who solo'd their way to a full Tals or Ik set, let alone a full runeword build.
Edit : I have discovered however, skimming patchnotes in patch 1.13 (2010) they made a lot of changes and upped the droprate on High Runes, so maybe these days my perspective is off. My opinions are based on mainly patch 1.10 and 1.11.