I'm not sure Kate is bland. I don't think she has a great work ethic, nor do I find her particularly talented - cooking & baking & getting along well with people are all things most of us were quite good at 20, let alone 40 with every possible advantage at our disposal - but bland, not quite.
I think Kate's public persona is curated, crafted and tweaked completely based on what the RF wants and by extension, what the public expects. After Diana, and as reiterated by Meghan, spouses who rock the boat are simply incompatible with the royal framework. If pigs could fly tomorrow and the RF decided they wanted to be fun and entertaining instead of stuffy and traditional, you bet Kate would be out by the end of the week wearing a sparkly leotaud and her tap dancing shoes.
She is what THEY want and she will always, ALWAYS comply. Partly because she is supporting William but IMO, Kate is determined to be Queen at whatever personal cost. She will never jeopardise that and William wants to be King, so they are very compatible in that sense. I actually think she's quite calculating and is disciplined enough to give up anything and everything that may compromise her position...and that's certainly not a bland person.