Now hold on, you made a claim, and I asked what practical experience you've had. If you genuinely have had lots of experience with higher end, properly fitted rifles, I'll gladly retract my earlier statements. But with that in mind, can you honestly say that your factory marlin, when fully loaded, handles better, is better balanced, comes up easier, points better, and has a smoother action than your custom Cooper? My experience with Marlins is they are very functional rifles, but the action is clunky (this is, admittedly, debatable as I'm not the biggest fan of lever actions), they don't point very well, are poorly balanced and don't swing well when loaded (mainly for models with full length magazines). They're handy and lightweight, and I generally like them, so don't think that I'm trying to say anything that's not a $3000 custom rifle is crap, because that's not what I'm saying at all.
It's not explicitly about how much it costs, but you do get what you pay for. Like everything else, there is the law of diminishing returns.