Is there such a thing as a dish being bland from too many flavors?

I think the description you're looking for is what is often described as "muddy flavors" or "fighting flavors" or "muddled flavors" (though the latter is also a term used for a specific technique, so searching the internet will give lots of results for that).

This doesn't mean that it tastes like a mix of dirt & water--but rather that the flavors are no longer distinct, and possibly fighting with each other.

When you create recipes, the goal is to get all the individual pieces to come together to "sing" like a harmonious chorus. Each element comes together to do it's individual small role so that when it comes together it create a beautiful song. If you use too many strong flavors, they fight with each other--like trying to build a choral group out of egotistical soloists who all want to shine as the center of attention.

That "group of egotistical soloists," in food, creates "fighting" or "muddy" flavors.

With your longer description, I can understand where you are coming from and why you don't like this version of the dishes (and also why somebody else might prefer them). But the term "bland" you chose is unfortunate, and is predestined to create misunderstandings.

"Bland" is a word with a rather well-circumscribed meaning, and means that there is an absence of taste and flavor. To use your color analogy, "bland" would be applied most directly to something that is ecru colored, and, less fitting but still understood, to something that has its own color tone but so little pigment that it is still nearly white. For food, imagine maybe a pudding made with starch and water, nothing else, that would be a quintessential experience of bland food.

The experience you describe doesn't have a unique term, and the descriptive ones I can think of are non-technical. The most specific one I can come up with is "mingled flavors", although this one doesn't strongly evoke that the speaker disapproves of the extent of mingling. You can choose whatever you like and best reflects your own subjective experience. Some examples would be to call it "conflicting", "chaotic" or "overwhelming" taste combinations. Or, if you prefer to continue the metaphors from other senses, you can use "cacaphonous taste" or, more diplomatically, "lack of contrast".

I would also like to mention that your experience here does not validate hers, she is also just as right as you are, and finding a term will not lead to an agreement between you as to what the perfect dish should be. Every one of you has a set point for enjoyable taste, expects to find it in the dish, and is dissatisfied when the dish misses that point. What overwhelms your experience is well-rounded for her, and what is nicely focused to you is boringly one-dimensional for her. In keeping with your color comparison, insisting that only one of the two positions is "right" would be like insisting that painting like Franz Marc is "right" and painting like Caspar David Friedrich is "wrong", or the other way round.

I like the comparison to 'the colour brown' & yes, I would agree this is quite possible.
To try stick with this allusion let's consider a generic takeaway ['indian'] curry.

A poor one is definitely 'brown'. I'm with you there. It has no highs & no lows, it's all just a generic 'curry flavour'.

Contrastingly, a good one has depths & highlights.
It has a deep red, an undercurrent of dark, long-cooked flavours. Difficult to tell apart perhaps, but a depth that the rest of the flavours need to sit on.
Then some later additions - a little added garam masala, giving some quick-cooked higher tones, in 'orange'.
Above that, some highlights, occasional stronger tones of 'green'. Maybe a sliver of ginger added just before serving, a flash of fresh chilli, a cardamom you find as a surprise half-way through.
Then above that, the brilliant 'white' of fresh coriander [cilantro], tomato, a squeeze of lime, a few ajwan seeds sprinkled over, a bright side-salad, perhaps also with lemon or lime & fresh chilli.

One other way to ensure these separations of flavour is to make sure all your spices are actually new [I won't say 'fresh' because these are mainly dried] but supermarket spices do tend towards the bland, even when newly-purchased. Specialist grocers might be a whole different colour-palette. I swapped from generic supermarket to an online specialist a few years ago & the first thing I learned was to use less of everything, the flavours were so punchy in comparison.
The same with the fresh ingredients. Supermarket coriander tends to only be green in colour, & that's about all it adds to the food… some green colour. Good stockists sell coriander you can smell from down the street. Bright enough to make you blink ;)

Okay, take a curry with 10 different spices (each of which you are familiar with) for example.

Will you be able to identify each spice in the curry with just one spoonful? If there were only one spice, say pepper, it would be easy to identify. But with the 10-spiced curry, you will only be getting one tenth the amount of pepper, blended in with 9 times the amount of the pepper in different spices (assuming she used a set amount for spices combined).

So if your brain has a hard time identifying the ten flavors, how would you describe the taste of the curry? Every flavor you will be able identify in the mix will be muffled by every 9 other flavors!

It's not like your brain will automatically find another flavor with a name (aside from generic ones like spicy) to replace the mix, so yeah, I understand how you might find the curry bland in a certain manner, though it could be simply overwhelmed.

To be honest, I wasn't very aware of this until long ago when I saw a baking reality show. This one contestant made a cake with like 20 flavors; the judges weren't happy about that, and that almost caused him to lose that particular round.