The ratio of large to small caps is not large. One large cap for every ten or so small ones.
Remember caps are only one aspect of decoupling there is seriese resistors and inductors to consider as well.
An under decoupled system might work but be more prone to disruption by interference. It is only when you start testing the system in the presence of interference can you tell how robust it is going to be.
Getting enough decoupling in the right place accounts for over 85% of all problems in professional development of cutting edge products and warps responsible for more board revisions than anything else.