Think comparing it to Slammer is a bit too far, especially given that Slammer was a complete prototype and the use of air canisters for it was always (in hindsight) going to cause some problematic issues... Smiler doesn't really do anything too drastic enough (and some of the smaller problems like bolts popping out happen on any coaster, even if the company involved in the construction of this were absolutely terrible)...
Your problems with it can be pretty much attributed to most other Merlin additions, therein lies the main issue... Taking this quote out of context:
Could relate to Zufari, Sub Terra, Saw, Swarm, etc. Take your pick...
Merlin's budgeting for these attractions never seems balanced correctly... Especially when you end up having the budget for another ride slashed because some idiot did the ground survey for Smiler wrong...