They do still sacrifice damage in that Guardian Angel only has as much AD as a B.F. Sword, and no attack speed, on-hit effect, crit chance, etc. It has pretty bad stats, but now it's just something that an ADC can grab before it's super critical that they do so in late game when they carry team fights and have a minute-long death timer so they can be safer against AD assassins. Again, they do still sacrifice damage, but now it's something that has two components that an ADC would take: cloth armor to negate a bit of lethality, and B.F. Sword for the AD, instead of Chain Vest which is a bit too expensive for a purely defensive item for an ADC, and Null-Magic Mantle which is in the same place. Furthermore, tanks don't need a resurrection item (with relatively poor stats, heh) just like they don't need a Banshee's Veil, especially since Stoneplate also took over GA's old build path. It just makes sense to gear Guardian Angel towards the champions who really used it anyways, and not make them sacrifice as much of a lead to extend it--while at the same time giving them less tank stats from it so they're still squishy and are vulnerable enough to burst to want to buy GA in the first place.