Thirty years ago and more that might have been a valid objection, but at that time the alternatives weren't great either. No one has suggested running syslog over unreliable transport after that.

In fact, the queue management and at least the possibility of some rudimentary end-to-end cryptographic integrity checks are some of the stronger points of rsyslog. Splunk Cloud and Elastic, as far as I know, lacks the latter completely which rules them out as a single log sink for environments with that type of requirements.