In order of prevalence, here are the problems I've seen, with explanations following the list:

https://www.minisplitunit.org/

Spray foam isn't thick enough.

Spray foam installers missed some of the air leakage sites.

Spray foam installers didn't understand the building envelope and sprayed either too little or too much.

Spray foam contracts and pulls away from framing.

Spray foam isn't thick enough.

This is more common with closed cell foam, but it happens with open cell foam, too. Since closed cell foam has a higher R-value per inch, installers generally spray 2" in walls and 3" in rooflines to meet the energy code requirements of R-13 and R-19, respectively. (I'm not going to dive into the energy code here, but these numbers apply to many climate zones, the latter being allowed under the UA tradeoffs rule. See the Energy Nerd's blog on this topic if you want to argue.)

Open cell foam usually fills the framing cavity completely, so it's easy to tell if the installer has sprayed enough. Closed cell foam doesn't fill the cavity, so you've got to spot check in a bunch of places to make sure you don't get shorted.

The video below is from a house near Charleston, South Carolina that I visited recently, and you'll see that the homeowner in this case didn't get his money's worth. I knew immediately when I walked into the attic that something was wrong because it was hot up there. In a properly insulated spray foam attic, the temperature won't be much higher than the house temperature.

Seems odd a builder would say that. Is he talking about just the attic insulation or all the walls? Your question is vague but you did say "the entire house" and to do all the walls in the existing house would be stupid and expensive since it was built in 2004. If you're talking about spray foaming the underside of the roof deck it would depend on whether it's a vented attic or an unvented attic within the building's thermal envelope, and a hot topic concerning rot. Because I'm not an expert without the facts, or what you're asking, I'd even hate to speculate or give advice what to do. What I can say is this; Moisture from indoors can escape through open-cell foam and contact the cold roof sheathing and eventually rot the roof Regardless of the climate you live in, so you should use closed-cell spray foam for roof insulation, but consult an expert. Find one, pay him if needed and determine what needs to be done and the correct way, because the wrong way could be a disaster for you in the future,

Spraying the underside of the roof creates a conditioned attic. In that case, be sure all venting is securely covered and sealed.

Source

Oklahoma is mostly in Building Climate Zone 3 (only the three counties in the handle are in 4), so open cell under the roof is approved.

Energy Code Status

Costwise, it would very likely make more sense to simply continue with your unconditioned attic, adding whatever insulation is sufficient to at least bring it to current Code standards in your county.