The E170/190 were certified to do the steep approach into London City, whereas the E175/195 are not, because the relative placing of the main gear and the tail on these two slightly larger (175/195) variants gives issues with tail clearance tolerances on touchdown when rounding out from the 5.5 degree descent at the required speed. Embraer actually spent quite a lot of money doing the steep certification of the 170/190 and understand well what will work and what won't.
Nothing to do with runway length, engine power, or whatever.