It sounds like a stiff master cylinder, which happened to me on my second water-bled brake.
There are two solutions. The first one, which is only really temporary, is to blast a load of oil into the master cylinder from the outside. This used to work for me, but only for a week or so.
The second is something I've never done myself, but I've seen it suggested as a solution for other people in your situation -
Disconnect the lever from the brake, poke/pull the plunger bit out of the lever, lube it up inside, and you may as well lube the seal too. Put it back together, all done, then go follow my bleed guide again!