His credibility is in no danger at all as far as I'm concerned. That is mostly a throw-in sentence. Think of the second part as it will take [at least] three times and be done with it. The main point he is making, I believe, is that hiring extra programmers does not counterbalance the use of ineffective tools. Whether the relation of code size and development time is linear or exponential is only of secondary importance to that statement.

Makeshifts last the longest.