Basically you want Apple to have hired SEAL team 6 to kill off Samsung's executives and engineers. That's really all they could have done other than what they did.
Of course they could. They could have put out a midprice and/or low price option to blunt the entry of Samsung (and others) into the marketplace. Allowing them in does more than just siphon profits, it allows Samsung (in this case) to devote profits to chipset design, display panel improvements, other internal features (NFC, etc.) and it creates a wealth of opportunities in the retail chain, giving incentive for vendors to open stores, kiosks, and for carriers (with hidden rebates) to push Samsung models over Apple's.
Yes, that means some models with fewer features (like the iPod nano vs original iPod, or the MacBook with a plastic case vs the MacBook Pro) at lower price points, but it's a very large segment of the market which Apple has simply GIVEN AWAY by not competing in it. The reason for their dominance in iPods was because they brought out models to cover every budget. With iPhones (and now iPads) they have, for some bizarre reason, chosen to serve only the high end. Well, you can be Mercedes if you want, but you are not going to have the profits of Ford, and eventually you are going to be a niche provider.