IMHO, the halved caster level and limited abilities by level (at least in 3.0) of a ranger and paladin come from the fact that they were probably originally designed as PrCs for the new edition. That's conjecture, but it logically would make some sense given how they (especially the paladin) are designed. IMHO, the paladin makes perfect sense if you either a) allow it as a 10-level fighter PrC and give it spellcasting and ability progression along the lines of the holy liberator or 2) make it a fighter/cleric PrC as it works either in Unearthed Arcana or in some of the house-ruled paladin PrCs that have been floating around the web practically since the release of the 3.0 PHB. It's really the 20-level nature of the class that I find a handicap, IMHO. A fighter/paladin/cleric, or a paladin/Fist of Raziel, is actually quite competitive with a fighter (arguably even more powerful) against evil opponents, and absolutely superior against single, magically-capable, evil opponents. The problem is that the Pal20, sorta like the Ftr20, isn't a very viable character build.