Wikipedia claims reason for the linear motor on the Oedo line was a smaller loading gauge and therefore smaller tunnels required.
And generally speaking 5 % wouldn't be considered very steep at all by modern standards. Gradients up to 4 or even 5 % weren't uncommon even on older rapid transit systems dating from a century ago, and for modern multiple units I'd regard 4 to 6 % as about par for the course.
And in hilly terrain, a number of systems definitively go beyond that into the 8 – 10 % range, including some new built systems (e.g. the light rail systems in Stuttgart, Tenerife and Jerusalem).
And generally speaking 5 % wouldn't be considered very steep at all by modern standards. Gradients up to 4 or even 5 % weren't uncommon even on older rapid transit systems dating from a century ago, and for modern multiple units I'd regard 4 to 6 % as about par for the course.
And in hilly terrain, a number of systems definitively go beyond that into the 8 – 10 % range, including some new built systems (e.g. the light rail systems in Stuttgart, Tenerife and Jerusalem).