MT tires definitely tear up mileage. But I'd also look at the tire size difference. Look up the actual outside diameter of the stock tires vs the MTs, then multiply your mileage by that ratio.
The MT tires are likely closer to true size, where the SR5 "31s" are probably more like 30.5.
I'm not OP, but personally I'm critical of all my vehicle purchases. I've never understood folks who are like "well, I spent 50 or 70 grand on this therefore it is great and we will speak no ill of it!" I don't attack other people's stuff like this, but I see no point in lying to myself about...
BTW wonder if your 4Runner just got "cleaned"/PDI'ed by dealer with some lousy products. I think those red glove boxes and center console covers would be the same part number.
Have owned both 3rd gen Tacoma and 5th gen 4Runner (still waiting on my 4th gen Taco order.) There is no comparison between those two vehicles on interior quality. For their vehicle category / price points, the 3rd gen is at the bottom of the industry and the 4Runner is at the absolute top.