I'll be honest. I care very little about things like bell curves, fidelity, etc. What I care about is speed. Optimize the hot path, and the core resolution mechanic is as hot as it gets. The more operations (especially table lookups) you need to accomplish the core "did thing succeed" meta-task, the fewer actions you can take in a fixed-length session. Which means more time sitting around waiting for things to resolve and less doing things.

NdX roll under? Fine. As long as any potential modifiers are written down and (at the timescale of most operations) fixed. d20 + mods vs static TN? Fine, with the same criteria. NdX vs fixed TN? Probably ok. Dice pools can work (because counting successes is fairly fast), but if every attack (to take one example) needs 4 rolls and decisions about how to split your dice pool (how many to block, how many to hold for another attack, etc), no thanks. Conditional bonuses, conditional rerolls (including exploding dice)? I'd rather avoid those. When the resolution system is invoked, all the decisions should have been made and it should just resolve. I care less about piloting the rules and more about what's going on in the game's fiction itself. The resolution system is there as a tool to be used to resolve uncertainty, not the primary draw of the system.

And anything involving looking results up on tables, especially conditionally (where deciding which tables to reference is influenced by results from a previous table lookup) is just flat out. Table lookups either require massive delays (orders of magnitude slower than other operations, similar to having to reach out to the network instead of looking in the processor cache) or holding tables in memory (which has major mental overhead and often requires falling back to physical tables because memory is faulty). Tables are fine for rare or asynchronous things (things you can do ahead of time, like random loot). But not on the core resolution path.