The first quote is generally true. I'll add some clarification to the second based on my experience.

There are plenty of entry-level CPA candidates coming into the field, and the supply of junior associates seems to be quite plentiful. However, the industry experiences high turnover among the ranks of those with less than 5 years of experience. Thus, the "shortage" is more so among the senior folks with certain industry or tax specializations.

So, a good "backup" career? I think so, as long as you plan to stay in for a while. But as far a supplemental income is concerned, it is difficult (perhaps impossible) to get lucrative consulting or tax work unless you have a certain amount of training and experience, usually obtained from work with a larger firm. Successful part-time newbies in the accounting trade are likely to offer bookkeeping and/or tax preparing services - neither of which require a CPA license. Building a practice from these two offerings can be quite viable, and ambitious practitioners can certainly replace their aviation income over time.

Just my buck-oh-five.