Two immediate responses .... you have enough teeth to make forty sets of dentures, and that derailleur is frighteningly close to being a kickstand.
Dentures!
That, my friend, is what a 12-46 cogset looks like when mounted on a 20" wheel. This was never intended (by me) and happened as the result of a complicated miscommunication. I took my recumbent and Mrs. Newleaf's unicorn fat bike in for service at the same time. This setup was intended for her fat bike, but ended up mounted on my 'bent. I have the exact same hardware on my touring bike and love it. I felt it would make a great difference on Mrs. Newleaf's 26" fat bike, but it proved incompatible.
I chose to keep the setup to see what it felt like to ride. Partly because the 'normie' hardware I needed was then on indefinite back order. The bike already climbed like a champ with an 11-32 cogset. The 12-46 cost me a bit of top end, but I can still hit 35mph easily enough. With the 11-tooth, similar effort on the same hill netted a bit over 40mph. Then it felt like it'd spin out somewhere around 45mph. The low end is just crazy overkill on a wheel this size, as expected. Even as much as I love crazy low gears, 46 teeth on a 20" wheel is just too much.
Your point on the derailleur is also well taken. A long cage on this wheel is not what I'd call wise. I've never liked it but chose to give it a try. A saving grace is that thanks to the crazy low gearing, I spend most of my time in higher gears, even on hills. Nevertheless, I think this part of the drive train will not be a part of this particular bike for long. I think an 11-36 might be more appropriate to the wheel size.
At first reading,. I thought you meant she stole one for you..

Apologies for my clear-as-mud prose. That is most certainly not what I meant

. It was delivered by Blue Santa, aka Amazon.