For next time: it's really easy to accidentally ruffle feathers if you come in and start proposing tooling or process changes. People get attached to their project if they've worked on it for a while, and can take observations from an outsider as judgemental or an attack, regardless of how valid those observations are (many of yours seem valid to me). You coming from big tech can make people even more sensitive to this (if you're triggering their latent impostor syndrome or whatever as someone from a prestigious company). The way you summarize your manager's feedback makes me think that you either rubbed him the wrong way or offended some more tenured people who complained. Kind of hard to undo that now, but helpful to keep in mind for the future. If you demonstrate that you can hack it on tickets as you ramp up and establish some trust with your teammates over a few months, you'll typically have an easier time with this type of stuff.

(I would normally add a caveat that another good reason to wait a bit before bringing stuff up is that you might be missing the bigger picture, and that can help you ensure that you're actually arguing for useful change. I omit it for you because "we should have any observability at all for our production application" seems pretty uncontroversial to me and doesn't make me think you're out of touch or focused on unimportant things)