I assert that this is a hasty generalization, one that contributes to frustrating and unproductive shouting matches, rather than actual discussion.
You can design systems that make such "tweaking" only necessary for edge cases, rather than a constant "it has to happen in every game, frequently, with only intuition as your guide."
One of the greatest failings of 5e, indeed one of the few failings I consider to be utterly objective, completely unrelated to what I prefer games to be designed for and instead an outright "this should never have happened" problem, is that it is just really, truly awful at providing DMs with tools and useful, concrete advice. This extends beyond the books themselves and to the community at large; for several years after release, the most common response to any thread or reddit post of someone asking a rules-related question was either "you're the DM, you figure it out" or "ask your DM, it's their job to know." Both of these answers were, of course, completely useless every time it was a DM asking this question, and yet the people saying it would more often than not double down rather than, y'know, trying to build and teach.
So yeah. 5e was designed in such a way that optimization is still just as prevalent as it ever was, but DMs have fewer and less-obvious tools for addressing those problems, and the support and advice to help fresh-faced newbie DMs get into it simply not very good.
But I guess they had to avoid as many 4e-isms as they could, and "giving DMs really really good, effective advice and highly functional, flexible tools" is pretty clearly a 4e-ism.