Going to be honest, being from Hamilton and going to school in Waterloo, this is both meaningless and fairly unconstructive as a post because of how different these cities are, and what the point of this forum is. As much of the other commenters have shown, there is significant nuance to what makes a city 'good', and certainly more criteria than what is being looked at.
I am going to speak from a mix of first-hand and objective POV. Firstly, being in KW makes you realize that the city is booming, which obviously is why Hamilton is getting left in the dust. There is more money around to do things that make it feel nice, and new development is really good at affecting people's perceptions of a place. The iON is a big piece of this, but as commenters have said, most of the development around it has come after it was built. Clearly, if the market sees something in Hamilton before we even have shovels in the ground, then there is something innate to the city that is desirable about it, not just explosive growth or new transit to leverage.
I agree with that market sentiment; Hamilton has the best urban bones in this province outside of Toronto, and in my humble opinion can compete in at least a handful of dimensions. Hamilton slowed down and KW picked up since WWII, but you can't change history. If people want those organic urban environments, KW is not going to scratch that itch the same way Hamilton can; we do so almost against all odds given the state of the public realm. There manages to be plenty of activity around, yet by every statistical measure the lower city is still nowhere near the population of the 1970s, never mind the 1950s.
Speaking of metrics, let's not assume urban growth always accrues velocity- no city's future is guaranteed, so I don't want to give to much credence to who is projected to be bigger than whom or who has more towers going up; Hamilton has one single downtown, KW-C has three and some change. None of them could become as vibrant as downtown Hamilton could- its just a matter of size and dispersal. If you appreciate growth at all scales, KW cannot compete outside of skyscrapers. Furthermore, I have more confidence in Hamilton's long-term stability based on what's being planned in terms of industry. KW, as a University/Tech town, runs the risk of becoming dependent on one industry for growth. We've been there, done that. In any case, I don't hold my breath for 50-story towers in Cambridge.
And let's be clear; KW-C is/are doing exactly what every other growing municipality with money in this province is doing- bike lanes, transit service, and planning density. But with that comes a lack of experience in doing things well, and a big capacity for missteps. It is not cash-strapped Hamilton that struggles with implementing bikeshare programs. Is anyone going to make a thread saying "wow, Richmond Hill is decades ahead of Hamilton"? Because Highway 7 is certainly a marvel, but I wouldn't call it good. Likewise, the iON is great, but its utility as a transit service is secondhand to being a development stimulator. And the student housing compound is extremely depressing once you get an eye for what cheap architecture and public realms actually look like.
Frankly, though (and I think this is the most important part), Hamiltonians don't really think about KW at all... we are more preoccupied with comparing ourselves to Toronto. Who we view as our peers is completely different from KW (often places in the US), and the things we do (and how we do them) are often completely different. I think It's a situation where the realities of places are so disconnected, and visibly so, that even if on paper they should be comparable, under the hood they are not at all. This is not to say KW is bad, or that you are wrong for thinking what you do, but only on the surface level could someone's takeaway from KW be that it is a place Hamilton could even compare itself to, much less try and learn from or compete with.
Something that will dispell this myth of whos growing and who isnt is looking at the UT development map. And yes, it does update for KW fairly often:
https://urbantoronto.ca/map/