In looking at the songs you've mentioned... My Generation... while it may be something as far as the first prominent bass guitar solo in a pop/rock hit... melodically, there's nothing particularly memorable about it. What he's playing during the song fits- nothing particularly groundbreaking- even for the time.
Substitute... it just rolls right with the changes- yes, it suits the song- best part is during the solo section. Nice tone though.
Who Are You... again, during the verse- it just rolls with the changes... during the chorus- it's just octaves. Yes, there's slightly more to it- but no more than Wyman pulls off in Tumblin' Dice.
To say he's got tons of memorable melodic lines, but to not be able to remember any of them? Where's his Penny Lane, or Tom Sawyer or I Was Made To Love Her or even Freebird ending?
I'm not saying Entwistle was a bad bass player- just that his rep comes from playing extraneous bits, and not playing melodic parts that support the song or move the song along.
Melody... even the bass line to Substitute is a melody- or enough of a suggestion of one within it's context- that that's partly how I identify with it. I guess we call that a motive or a figure in practice- a melodic fragment, to be liberal!
So I guess in an argument you have me called up short on my abbreviated "memorable" list, but finally I don't think that melody is necessarily what makes a bass line; it's merely an attribute to one's playing that may or may not be outstanding. Even though "Tommy" has a nice ditty moving along on the bass... ("Tommy can you see me?...")
But the thing that made the Who work in the rhythm section was the way Entwhistle and Moon worked together- like a cripple and his helper winning a three-legged race in the Olympics. Personally I think Moon was most responsible for the sound of the Who- but that's another instrument, isn't it...
Come to think of it, I agree with you at least in part. The Ox
noodled, though he was very good at it. He even said he wanted to make the bass sound like a guitar- but I still like the propulsive and forward-feeling notes of the line to Substitute. And even the octave pattern in Who Are You pushes the thing along. Despite the static ostinato, it doesn't feel static- it runs.
As far as Jack the Bruce, there's no accounting for taste. And the fact is that, like him or not, he's still going to get credit for being a groundbreaker in the suddenly expanded role of the bass, because he
was a groundbreaker. It's difficult to overrate that, I think. Dig the live "Crossroads". It's good jam.
I love Jack Bruce, but some friends and I were listening to a live recording of him doing a solo. He must have been "off his horse"

, by virtue of the addling, pedestrian triplet pattern he'd gotten himself stuck in...twice... one of us finally shouted from the couch, as if from the front row of the audience, "Finish up!"
Rate 'em high as you want, nobody's perfect. These guys still deserve their fame!
Keith Richard is also responsible for some of that Stones stuff. But I know what you mean about the economy there. It's not even the space that surprised me as much as the note
choices- and
where they went! Jumpin' Jack Flash ain't no garage-band sing-along. Yep, Wyman is a bad dude. So is Keith Richards, Ron Wood, and the Faces' Ronnie Lane! Check out "You're my Girl, and I Don't Want to Discuss it!" on Gasoline Alley... I digress...