When Mooch did the real world test, it turned out that the difference in voltage drop between the Admiral in brass and in copper was 8 milli-volts vs 7 milli-volts so only 12.5 percent less voltage drop going from the brass to the copper. His testing was done with a 30A load, so about 110 watts. At 30A, 0.007 volts voltage drop translates to a power loss of only 0.21 watts, whereas 0.008 volts voltage drop translates to a power loss of 0.24 watts. That's only a 0.03 watts difference. So the reason why you aren't gonna notice this 0.03 watts difference is simply because, if you're vaping at 110 watts, there's a really, REALLY good chance you aren't even going to notice a 0.3 watts difference, let alone notice a 0.03 watts difference. That plus the fact the difference between copper and silver is even smaller than the difference between brass and copper.
But some people still like to brag because they keep wanting to believe in Black Magic. Your story about the ramp up time is just an old fantasy tale because, vaping at 110 watts, a 0.03 watts difference equals only 0.00027 percent. Before we can talk, let's see you feel a 0.01 percent difference first. lol.. just lol
Solid pure silver contacts do matter. As for the maintenance, that is, and also if the button contact and/or firing mechanism has been poorly designed and/or mishandled, much to the point of solid pure silver being capable to be used to try and "cover up" the fact, i.e. by curing symptoms instead of by addressing the root cause of the problem. But using solid pure silver for the body of the tube mech mod? No. The wall thickness of the tube would have to be almost as thin as tinfol before this difference in voltage drop will become in any way noticeable by vaping. If it is at least a few millimeters thick, then no. Simple physics is simple.
As for "21700s hit harder than 18650s", yes the 30T does hit a bit harder than the 20S, as the test results from Mooch clearly show. But you might not notice it in practice. The higher you go up in coil resistance, the smaller the difference becomes. This is due to the fact a higher coil resistance causes less current to be drawn from the battery (i.e. the load drops, and so the voltage sag also becomes smaller as a result). I do notice the difference on a single battery tube mech with a dual coil aliens build at 0.11 ohms, 27/36 Ni80, 4.5 wraps, 2.5mm ID.
This doesn't stop me from using the 20S in a single battery tube mech, though. (I use both the 30T and the 20S in my single battery tube mechs these days, even though previously I used to prefer the 20S for that, but these days it just depends... like, it partially depends on the choice of atomizer, the drip tip, or actually the height of the drip tip.)
Further, the battery orientation thing goes as follows. First, consult the official documentation of the mod when possible, or else just ask the manufacturer. Failing that, the general rule of thumb is to put the positive side of the battery closest to where the vent holes are. The reasoning behind that general rule of thumb comes from the fact a battery can start swelling due to high pressure buildup inside the battery before it vents, and, because the manufacturers know that mech users don't like battery rattle, they usually design the mods to have very little amount of spacing between the wall of the tube and the side of the battery. So if the battery swells inside the narrow tube, it closes off the only trajectory between the vent holes and the pressure escaping from positive side of the venting battery, thereby it renders the vent holes useless.
Another thing to also be aware of is, if the inside of the tube doesn't have an insulator lining or sleeve, then if you put the battery upside down, any damage to the side of the battery wrap can immediately cause a hard short because the side of the battery is negative whereas the whole body of the mod is─due to the battery being upside down─positive. However... torn battery wraps are ALWAYS a recipe for disaster no matter what, so don't let the presence of the insulator lining or sleeve be your pretext for using a battery with a torn battery wrap. Just be aware that a battery wrap can get damaged by rubbing against something sharp inside the mod, and that this can affect the final risk outcome if the battery is upside down.
On a hybrid or direct-to-battery mech mod, use an atomizer with a protruding 510 center pin. On ANY type of mech mod, NEVER use a tank with a drop in coil; drop in coils typically contain a silicone/rubber insulator that separates the positive contact from the negative contact, and that can potentially collapse UNEXPECTEDLY and in such a way that it might cause a hard short DURING normal use. Coil build absolute permanent stability is always compulsory on every mech.