At What Point is a Solid Cam Better Than a Hydraulic Cam??

That's what I've come to understand. A lot of modern OHC engines use solid tappets with the only adjustment being from replaceable lash caps and they only need to be changed during a rebuild, and at that usually only when changing to a bigger cam and/or installing new valvetrain parts. Buddy just went through it on a Ford 2.5L Duratec I-4 he swapped into his NC Mazda Miata, this is stuff made in the 2010s.

We would adjust the the rockers around every 100,000 miles. No high pressure springs, no "fast" lobes, 30 wt oil with zinc.