Avios definitely disappear more quickly than they are earned, especially if you are doing a full-blown redemption rather than just using them to upgrade. I recently redeemed 70,000 Avios on two return trips LAS - SEA - ANK / ANK - PDX - LAS as the cash price was absolutely ridiculous, along with a further 30,000 for a LAS - PHX return for two on the same basis.
I think I had something in the region of 500k Avios at one point but nowadays the balance is usually considerably lower. Earnings are down too mainly due to buying AA tickets rather than BA. As a result you don't get the cabin bonus, although - again - the cash savings were significant.