Unrenewed certs have not caused the kind of extended mass outages DNSSec has, it's not close.
There are also operational risks, as Let's Encrypt has to have their secret key material in close proximity to web-facing services. Of course, they use HSMs, but it might not be enough of a barrier for nation-state level attackers.
The offline signing feature of DNSSEC allows the root zone and, possibly, the TLDs to be signed fully offline.
That's why in my ideal world I want to keep DNSSEC as-is for the root zone and the TLD delegation records, but use something like DoH/DoT for the second-level domains. The privacy impact of TLD resolution is pretty much none, and everything else can be protected fully.