there is no typical gradient or length, at least not for me

talkin 'cassette' without talkin chainrings is fairly useless - ultimately if you want to discuss gearing you need to get to gear development, or for olde phartes, gear inches...

blame the bike or any component however much you want. however it sits quietly in the corner regardless of the blame heaped on it... blame the motor

every week I go for my weekly hill climb. It is 3.2 mi long, avg gradient of 7.5% (with bumps to 16% & 12%), I do it 2x. Every week I say to myself "I'm gonna fly up today!", every week, about 1/2 way up, my heart is poundin in my mouth and I'm hardly flyin... defective motor...
sometimes I'm less slow... sometimes it seems eternal.

I ride a triple 52/42/30 with a 13/14/15/16/17/18/19/21/23 (9 spd) or a 53/39 with a 13/14/15/16/17/18/19/21/23/25 (10 spd) which, on long uphill drags usually means I ride low 50 to 40 gear inches.
Sadly, I find myself finding the 34 or 36 more often than I have in the past.

ymmv