Thanks Steph I see what you mean. The answer is really that there is no clear answer because it is a question of nomenclature and there is no 'technical' definition of 'latte' in this context that I know of. What you are really asking is what is the best option or something like that? It seems to be a feature of language that people think of terms and words in relation to what they consider ideal or 'normal' cases, other factors cause terminology to vary widely and there is no Academie francais or ISO body to pronounce on this one. Even if there was usages would still vary as Academies and language mavens everywhere eventually learn. Ingredients or components often become names for foodstuffs or well used items, 'latte' being the best example, "chili" another, "canvas" on sailing ships yet another.
Nomenclature regarding coffee in my extensive experience varies widely but is often taken very seriously 'locally' you might say. So it depends where you are, even then there is not agreement. In London for example experienced Italian Barristas disagreed with local coffee shop owners: whose opinion do you take? I normally use the 'when in Rome rule' but didn't in this case, considering the barristas to make a better result and nodding to that I guess?
I was served once, in Cardiff Wales in Cardiff Central Market when I ordered 'Cappuccino', a large mug of lukewarm instant coffee with a 'head of synthetic cream from an aerosol can and some fake cocoa sprinkled over it, mostly on the handle. As a linguist professionally the question is interesting to me as to whether this abomination should be included within the range of the term "Cappuccino". Any takers? Same applies to 'latte' over all I don't think you can relly on much more than getting milk in some form or in some quantity with your espresso.