CPPI is not the usual form of capital guarantee. CPPI is offered on funds generally, because it's hard to buy derivatives on a fund like you can buy derivatives on an index. CPPI is an algorithm rather than a financial insturment.
You are correct. A normal tracker (not cppi) has a return which only depends on the where the index ends up, not on how it got there. But cppi's are path-dependent, an early market fall will cause the cppi to underperform. If the market went from 100 to 80 to 140 the cppi would significantly underperform the case where the market went from 100 to 120 to 140. In extreme cases you could be locked into the riskless assets (bonds) at an early stage, then you're left to wait till the expiry of the cppi to get your original money back, while the market could be roaring ahead.