Why T-Shaped People?

If your product can be built entirely by "t-shaped" people, it's not a complex product.

The thing about experts is that they're experts, an expert is INCREDIBLY good at one particular thing.

The idea of "t-shaped" came about as management didn't want to pay for "full-stack" people.

You know, people who are very knowledgeable in the entire software stack your product is built in (But are also experts on one particular thing)

Today it's a SCRUM sales pitch, that you can do more (development) with less (people) and thus save money.

What you're really doing is overloading the people you have, and usually expecting them to all perform at the expert level.

"Bob can do this in 2 days, why do you need 7?"

Almost no project has no "crunch time", and crunch time means you need to fly as fast as possible, you can only do that when everyone is assigned work within their area of expertise.

If you need experts, get experts, don't get fooled by the "Agile" sales people.

Remember, the agile manifesto is only a few lines of text, anyone selling you courses and books are doing just that, selling you stuff.