Nah, that's not fair. Now is now, then was then. And back then the Civic Center was a visionary part of a very visionary phase around Charles Center. It was also a big phase of Rouse getting cranked up.
Back then, multi-purpose was a forward looking idea. It opened in the early '60's but was one of the results of a mid-50's effort of civic leaders to bring and keep life in the City, the Greater Baltimore Committee. That whole effort was the same kind of "for the greater good" thinking that got civic leaders behind the idea of buying the St. Louis Browns. Fortunately, their focus on redevelopment was way ahead of its time. By the time Charles Center happened, the City really, really needed a shot in the arm. The only reason it happened was because they started, not just noodling, but doing actual planning back in the 50's, which was way before the idea of "Urban Planning" really existed. The Inner Harbor was like Phase II of that project. It had credibility mostly because the whole Charles Center thing worked as well as it did.
Now, it is true that people could and did critique the design of the Civic Center from the get-go. Various details about it could have been better. But how much did anybody really know about arena design then? And it definitely would have been crazy to build a 17,000+ seat arena back then. Nobody went to basketball games then like they do now. Nobody could fill a concert hall then like they do now. Almost nobody had big-crowd things like they do now.
Then why build a 14,500-seat concert hall? That's essentially what the arena is.
I realize that I'm looking at this from a modern perspective, and things were very different back then in terms of civic planning (this was the same group of people that was going to build I-95 through Fells Point, across the Inner Harbor and through Federal Hill). However, there are plenty of examples of arenas built in that era (and even well beforehand) that could be used for many purposes but were designed in a fashion more like modern buildings, and with large capacities.