All of that is a very typical Django stack with React bolted onto the frontend. Whether he runs into trouble managing RabbitMQ, Redis, Postgres or any of the Python services is another story, but at least if he did there are many, many others using the exact same stack, so he should be able to easily find answers to people experiencing the same problems. All of these technologies have several year track records now, too, so (hopefully) they are stable and reliable in production. My biggest concern would be managing the ES cluster.
On the other hand, I disagree with his points about docker being overly complex. Docker images are simple. Kubernetes, once you get the hang of it, is great on GKE and gives you automatic SSL via Google or let’s encrypt, and load balancing and auto-scaling just works. It’s probably more expensive than managing your own servers, at this level, but maybe not since you could pack more services into fewer compute instances.
All the things they mentioned:
Ubuntu, PostgreSQL, Elasticsearch cluster, Redis, RabbitMQ, Django / Python3, uWSGI, Nginx, Celery, Celery Beat, Supervisord, React + Redux + Webpack + ES, Amazon S3, Cloudfront, react media player, Ansible, Datadog, PagerDuty, Rollbar, Slack, PyCharm, MacBook Pro, Vagrant + VirtualBox, GitHub
WeWork, iTerm2, tmux, Notion, G Suite, MailChimp, Amazon SES, Gusto, Upwork, Google Ads Manager, Carbon Ads, BuySellAds, Cloudflare, Zapier, Trello, Medium, GoDaddy, Namecheap, Stripe, Google text-to-speech API, Stripe Atlas, Clerky, Quickbooks, 1password, Brex, Bonvoy Amex card, Capital One Spark