I agree that a tiny drain plug is not likely to have much impact. It's a good thing to catch big stuf before it goes thru the oil pump but that isn't an issue with all engines. A filter magnet might catch more iron than a drain pug magnet but in the end it's the return on investment (ROI) that often drives these discussions.
It's much like our discussions on primary filter efficiency. When you look at that objectively, you will see that below a certain threshold, improved efficiency doesn't usually pay the freight. It seems clear from statistical analysis, that with the low contamination input situations we here on BITOG normally encounter (it's different for off-road equipment that operates in total filth) that the "wear curve" really levels off below a certain efficiency point (which IMO is around 40 um absolute) and efficiency improvements below that do not result in equivalent wear reduction. At some point, the extra money you pay for the high efficiency filtration is not returned by a reduction in wear. MOney spent for very little. There are a few other benefits to high efficiency filtration that I won't go into but essentially, the ROI on a name-brand $4 is most often greater than a $9 one when the difference in price is mostly a difference in efficiency. High filtration is "better" but it really doesn't pay most people back in any tangible way.
I think the same thing is true with magnets. And I'm talking about not just a pencil eraser sized unit but something substantial. They are "better" but what you gain doesn't pay you back in most cases. The oil filter catches the bulk of the harmful material, iron or otherwise. The magnet catches all the iron but a good portion of that capability is redundant so only the small particles that the filter can't catch are the ones that "count"... but these are also the least harmful particles.
As with high efficiency oil filtration, the greatest benefits come way down the road. A normally maintained engine can last 250K miles these days. If you are like most people that do 12K miles per year, that's 21 years of driving. Will the rest of the car be a rusted out hulk by then or will you simply be ready for a new car? People who put 50-60K miles a year or more could benefit from high efficiency filtration or magnets because they have the potential to wear the engine out before attrition catches up with the rest of the car (or they simply want a new one) and the extra 150K reliable miles delivered by the improved filtration is a benefit.
I also think that the idea of using magnets should be evaluated according to the type of engine. Much of the "good rep" magnets have came from the old days. Older generation engines were all iron and they shed a lot of metal from their flat tappet cams, Morse or roller timing chains and ball pivot or shaft type rocker arms, not to mention low grade block castings and poor air filtration that made the bores wear like mad. All those engine features resulted in a great deal of iron in the oil and combined with relatively low efficiency oil filtration (compared to today) a magnet could pay for itself in fairly short order. Look at a UOA on an old smallblock Chevy if you want to see what high iron is all about.
In todays engines, beside the great strides in "everyday" oil and air filtration, most engines use external timing belts instead of chains, overhead cams, roller tappets and/or roller rockers and their block casting wear much less than before. All that results in much lower iron contamination inputs so a high dollar magnet is even more redundant.
On top of all that oil has greatly improved so even the old gen engine will produce less iron as a result of far better lubrication.
So, yeah, magnets are "better." Are they worth the extra expense to most people? IMO, no, but if you fit some of the special situations mentioned above, they might. You get to decide.
