Your data is very misleading as it is a function of timing. If you bought in Jan 2001, Mar 2002, Aug 2003, Jan 2007 or Jan 2008 You are losing as much as 40%. If you bought at regular intervales since its inception you are flat at best. Nothing to write home about. I vote to remove all board members.
Yes, you make a good point but your point applies to the majority of stocks and the broad markets - so why single out MENT? Personally, while I have been buying MENT over the last few years, I have done very well. So for me, I don't really see the benefit of Icahn's activity. It's fair to say that investing in the stock market in general since ~2000 has been a wash. In the decades prior to 2000, the trend has been onwards and upwards.
For my part, I wouldn't put my money into MENT for a 10 or 20 year investment. This just goes to show that your time horizon matters. Most people on these boards have a short time horizon.