Except that Tool never actively disbanded.
I know that doesn't matter for the years in between albums, but Tool literally took 13 years for a new album, whereas Porcupine Tree had about 10 years off. In terms of productivity, that does matter.
And yes, while 'Porcupine Tree' started in 1987, it was not until years later that it actually became a band, rather than a one-man project.