Long prerequisite chains suck. They suck bad. Why should I have to take 1-4 feats/enhancements/epic destiny abilities/reaper enhancements that I don't want, just to reach the one I *do* want? It limits build choice.
You want examples? Have I got examples for you!
Handwrap monks almost all take the exact same 10 heroic feats, 6 of which are prerequisites.
Greater two weapon fighting and its 2 prerequisites, whirlwind attack and its 4(!) prerequisites, stunning fist, and improved critical. The twf feats aren't *too* bad, as they are useful when you get them, but each overwrites the previous one.
Whirlwind is just egregious. Until the recent change to spring attack, I would not choose to take *any* of its prerequisites if I didn't need them for whirlwind. They all give very marginal benefits that I can live without.
Most other melees take 3 weapon style feats, when each just overwrites the previous feats.
Energy burst. It's a great t4 twist on any int/cha caster. However, if you're in draconic, it costs 9 epic destiny points to max it out.
Master of [spell school] in magister costs 12(!) points to max out
Sorcerer savant SLAs cost 9 ap to max out.
Efficient heighten costs 8-12 ap to max.
Lightning motes sla from artificer arcanotechnician takes 12 ap.
All enhancement tree cores require the previous cores.
In most cases, some or all of the prerequisites are taken only to reach the end of the chain, or players avoid the chain altogether because it's too expensive.