You might engage your architect in a frank conversation asking her what she is trying to achieve by hiring these professionals and what the benefits to you will be. It may be prudent if you are installing systems like in-floor radiant throughout the house or incorporating other new, green, energy efficient technologies with advanced controls.

SR

Mechanical, Plumbing. Electrical.

Not really that important on a typically sized residential job.

Even designers now how big to make wet walls and how to place them.

Mechanical often devolves into HVAC.

Unless you are planing a VERY large house the trade guys at a decent size company can do fine

sounds like architect is passing liability onto
MPE.

"We are looking into whole home radiant heat, wouldn't the manufactures provide support for their systems?"

Possibly at some level, but it sounds like the architect is not familiar and does not want the sole liability.

I'd think this is something a licensed HVAC contractor does to spec a job bid? Maybe not where you're located. Where is the house being built?

For $10k, I'd tell your architect you want three bids. Ask her to give you the relevant information and then you get the other two. Also, talk to a couple of well regarded HVAC contractors in the area who do the kind of systems you want, see how they operate in these circumstances.

There's enough monkey business that goes on in the construction world, I'd not dismiss the suggestion but I'd also not accept it immediately either.