The problem with that is there is a very clear policy purpose and interest in making housing an investment - the vast vast majority of people will eventually own a home, and it is a forced savings vehicle because people are REALLY bad at saving for retirement. Even if you fix our lack of a social safety net, home ownership is generally seen as a public good because it encourages people investing more in and caring about their community, being willing to pay higher taxes to support more services, etc. It's not a no brainer to make housing an investment (there are arguments against in a society with a good social safety net), but it is very purposeful through good public policy. It has little to do with the recent (very recent, relatively) buying up of single family homes by investment banks, etc, despite people implying all the time it's some secret cabal and shadowy wealthy figures doing it for their own benefit. Everyone sees conspiracies everywhere these days.
Of course, if we're going to say that home ownership is "good" and keep doing all the tax incentives for it, we do need to stop corporations speculating and driving up housing costs, and could do so by some targeted taxes on unoccupied properties in the same portfolio. But there's an argument to be made that that's a relatively small portion of the problem, since a lot of our housing stock issues can be traced back to single family zoning issues, as well as road and highway funding leading to suburban sprawl and unaffordable newly developed subdivisions while cheaper starter homes don't exist anymore...but either way affordable housing stock just hasn't kept up.
Did no one read the article? All of his complaints are correct! Replacing old city pipes, that are almost assuredly covered in years of internal layers to mitigate lead leaking, will have a negligible to possibly even negative effect on lead at the tap. Even Brookings said so in their study! Buttigieg is getting a total pass here ignoring the real issues raised by just rebutting about how lead is bad, when they're both saying that. So tired of people scoring cheap political points on soundbites, and Buttigieg doesn't usually fall prey to that sort of thing.
Yes, the funding should have been higher, but if we've only got 15 million to work with, it might actually make more sense to do targeted fixes in low income communities in old residential buildings, where you're most likely to have lead effects actually being felt at the tap from (relatively) newer lead pipe still in walls. But that would be expensive and much harder than just replacing water mains, so they're doing the easy less-important work first, rather than getting the biggest bang for their buck.