the tradeoff with regards to slower queries and io only comes into play if the TSDB is performing a narrow lookup on a handful of series. In that case it’ll be faster. But when you scale up to 100s of millions, columnar dbs like Parseable win because-

a) there's no per-series inverted index and labels are parquet columns so memory is not bounded by cardinality

b) data lives on much cheaper object storage (parseable gives an option to cache data locally to remove io bound latency)

c) columnar store helps with faster data scanning by aggressively pruning and filtering data out