There's a difference between algorithm hard and integration hard.

Algorithm hard: extremely hard to think about, but actually only a small number of lines of code.

Integration hard: obvious but requires lots and lots of glue code.

Two common errors:

See an algorithm hard problem and say "that's hard, we need 5 people"

See an integration hard problem and say "connect a bunch of backends? That's easy, we only need one person".

But the former actually just requires one person (although the right person).

The latter needs 5 people (but anyone will do).