The steel base plate doesn't double the magnetic field, it has very little effect on it. Because the permeability of the AlNiCo is rather low, there's very little reciprocal effect between it and the steel parts that are around it. Steel beside other steel has a greater mutual effect. The main reason they would abut AlNiCo with steel was to "keep" it, or help maintain it's magnetic field, but they wouldn't expect it to make the AlNiCo stronger than it would be otherwise. The steel keeper will have a magnetic field within itself, but if the steel is at the bottom of the pickup, it's essentially out of play, with respect to the guitar strings. Imagine the output you would get if you lowered the entire pickup to the depth of that steel plate, that's about how much it matters. If you're acknowledging that they're more alike than less, I'd agree, but since mounting Tele pickups in a Strat would represent a hassle unto itself, I'd say carry the philosophy a bit further and match the low Q of a P-90 with the tone knob, and the peak frequency with caps, and the low magnetic pull by lowering the pickups. Speaking in terms of the physics, what the Tele neck pickup cover does can be closely matched with the tone control, and what the inductance does can be matched with capacitance. What keeps people from turning to simple solutions is most likely psychological. There's no marketing machine for caps, or the tone knob, but there's a big marketing push for guitarists to buy new pickups, and the members on these forums play into that notion, too, when they get caught up in the enthusiasm.