Yeah, but remember the capacity is less a design flaw and more a compromise. The Civic Center and and especially the Colosseum were very concerned about having a facility in Storrs that could conceivably compete with them as a concert venue. In order to get the votes for Gampel the capacity was limited.
In addition to what you mentioned CL82, the entire fundraising effort for Gampel was a huge challenge at the time. UConn basketball had not even begun it's ascension to the level of prominence it enjoys today. Understandably, people weren't so anxious to pony up hundreds, god forbid thousands of dollars each to get this done. I believe the total cost was around $28M and the state was kicking in $22M, so even at 6M, it was still difficult and challenging to raise the private funds ...took quite a while. There were some who thought we'd never reach the target. Point being...it wasn't easy to get this done with the program's standing at that time. We really hadn't done much at all yet and hadn't even cracked the top 20 for a long long time.
The original building had only 8,241 seats. It wasn't until after the program really began to take off, which coincided with the opening of Gampel, that everyone wanted to go and the decision was made to use the expansion room in the corners to add another ~ 1,800 seats, to bring it over 10,000. So they did build in for some expansion, but with the stipulation the state put on the overall size, it was never thought of as being a 15-20K facility. The state didn't want to compete with itself...
In hindsight, it would have been nice to be at those levels, but it never would have been built at that time if those were the parameters. Amazing how far things have come in that time!