I’m not sure it is as big of a deal as people make it out to be. A 2 inch line at a decent slope is in some ways better because the smaller diameter will have a higher water level and thus push the solids along better. Of course at the end of the day it comes down to code, get the proper permits, do it to code and you won’t have to scramble to find and engineer and pull stuff apart in 10 years when you sell and the buyers bank balks on loaning money on a house with unpermitted work.