Trains can run every 3 minutes, that means the throughput of passengers is roughly 900 passengers every 9 minutes.

You're not getting 150+ cars in that tunnel during the same time period.

Doesn't look that way in the bay area on the caltrain line from San Jose to SF. Tere, due to limitation and NIBYism along the tracks, but part of the argument of the boring folks is that a tunnel would not face the same political headwind that a decent train system would require.