Why have a pop at someone wanting to instruct to build hours to then get an airline job when not long ago it was the main way to go from BCPL to CPL? ie 700 hrs.
When I learn't to fly, ever single instructor I had was building hours to move on. They may not have seen instructing as their calling in life but they adpated to it, acted professionally and seemed to enjoy it.
If you are going down the Ryanair/Easy/pay-for-your-type rating route, then FI will mean next to nothing. But there are still oufits that appreciate FI experience such as Eastern, flybe and many corporate/air taxi operators. You can also tick the 'in current flying practice' box rather than have to stump up for aircraft hire yourself.