Arduino and Microchip are in different markets. However, if you compare Microchip stock performance to Atmel's, they are basically unchanged over the past 12 months. Microchip (MCHP) pays 3.29% dividends and has capitalization of $9.2B, while Atmel (ATML) pays 1.98% and has capitalization of $3.39B. Atmel is smaller, but neither seems to be eating the other's lunch. Still, 3.29% is a lot better than 1.98% dividends.
BTW, I, too, am frustrated by Microchip's lack of support for MPLAB 8.92 and the difficulty/impossibility of using MPLabX with Assembly.
John