While the grammar cop in me yearns to agree, English is a language that evolves based on popular not proper usage, and the definition of "titular" appears to be evolving. It's common now in American dictionaries to find an adjectival definition of "titular" something along the lines of "Of, relating to, constituting, or derived from a title (as in the titular hero of a play)." I took a quick look and found such definitions in both Webster's and The American Heritage, as well as at Dictionary.com and a couple other online dictionaries. In some of those sources, that definition actually preceded "in name only."
"Eponymous" is definitely more clear and concise, but I suspect it's dying in American usage (I'm not sure about British usage).
But, hey, I'd gladly allow "eponymous" to be absorbed into "titular" in exchange for rolling back the madness of using "they" as a gender-neutral singular pronoun. Compromise!