Are lawnmowers built worse than 20 years ago?

Some engines specify cast iron sleeves which should be a better motor.

we had a 20 horse v twin kohler on a craftsman riding mower. When we bought it, someone had rebuilt the engine after throwing a rod thru the block. It broke a cam in 1 year and just utterly failed to run or have compression after about 2.

Now we have a 16 horse john deer not sure about the twin motor brand, that runs perfectly. We mow 5 acres of field like a bushhog.

I noticed the air filter and engine cooling fins get clogged up quickly. When I took apart the 20 horse kohler, the fins and little air passages (that pass thru the head around the valve area) were totally clogged to bejusus and back. I think this is the premature demise issue - failed cooling. Now after every season, I take off all the cowls and fully blow out all the air passages and fins cause they will be packed full of dirt and grass.