exhaust systems

[oj88]

in my opinion, if manufacturers designed their mufflers' insides right, and angled the descent of their mufflers into the tailpipe,
there may be little need to drill drainage holes.

The muffler is a chamber and it's installed almost always, horizontally. The outlet pipe is more often than not, higher than the lowest part of the muffler. It has to be standing vertically to make sure water doesn't accumulate.

With the heat and pressure of the exhaust gases, any condensation (likely minute anyway) will just dry off and be expelled later on.

Good point. Though water is a by-product of combustion so there's always a steady supply of it, however minute, every time the engine is running. It may be possible that high ambient temperature and high EGT is enough to vaporize whatever amount of water has collected. But that may be dependent on a lot of other factors.