Things are better now with Upwell 2.0 to remove low powered Upwell structures. A full powered Astrahus you need something like 5000 DPS to reach the cap and 500 DPS to prevent reinforcement. That means you need 5000DPS to reinforce it in 24 minutes, 2500 DPS will do it in 48 minutes, or 1000 DPS in >3 hours. If @Netan_MalDoran is right, then you can reduce those numbers by 1/3 (3333 DPS for 24 minutes) which is 3-4 gank fit battleships or attack battlecruisers, and they have to do it only twice.
The only problem comes if you think a defence fleet is going to show up, or the Astrahus is going to start shooting at you. In that case you would need a more balanced fleet with some tank and some dedicated logi. But if it is truly abandoned, then even a couple battleships/ABCs could remove one in a reasonable (30-40 minutes times 2) time.
EDIT: Since you asked about overkill, to be clear there is no use to bring more ships/DPS than you need to reach the DPS cap. The Upwell mechanics are such that whether you have 5 battleships (hitting the cap) or 500 battleships, it still takes a minimum of 24 minutes to reinforce. Additional ships are only useful if the other side shows up to fight.