The open source section of Gitlab is very powerful and perfectly usable on its own.

The problem with open-core licenses is that you always have to weigh the risk of whether the feature you depend on will get pulled into the paid license, pegging you on a release forever without updates.

If you look at the direction of most popular products that are open-core, you have a spectrum from ElasticSearch (Slightly hobbled, the free x-pack features that you WILL use in production put you at risk of dipping into paid uses and in violation. running Amazon's fork/open distro is strictly better) to Neo4j (completely unusable in a production context without a paid, mega-expensive, cost-of-a-nice-house-per-year license. No clustering, can't be effectively monitored, none of the tuning knobs that you will need as your dataset grows).

Open-core licenses are entirely hostile to the spirit of OSS and just pay it lip service to delude the ignorant.