2 or 3 games from a series in a gen isn't overbearing, as long as they can get the first one out early (and for it to be good).
The XIII situation with being so late into the gen and a big dissapointment with a quick cash in followup is definately not the way to do it.
But...that's exactly what they can't do. Last generation they knocked it out of the park with X, and while initial sales were obviously low for FF, XI became one of their most financially successful ventures in a long time. X-2 and XII were at least well-received at home. Dirge of Cerberus was really the only misstep they had with the series back then, but that's when we expected quality from the mainline games. A shit spinoff didn't quite hurt the series' image that much.
This generation they took far too long to release the middling XIII, the aborted fetus XIV, and the XIII sequel no one wanted. All while vXIII rots in development hell. They seriously need to shift their focus to quality over quantity. They have already destroyed any good will the franchise had left. What was once one of the biggest franchises for Microsoft to grab at the beginning of the generation has become absolutely irrelevant to most fans and the rest of the industry.
Time for Wada and Co. to get the picture and see that no one wants these half-assed games. They need to get their shit together with the franchise and they need to build up some new properties with some decent pull if they can't fix this issue and need to leave one of the landmark, iconic franchises in gaming history six feet under.
If XIII-2 at least managed respectable sales in Japan I'd have a different sentiment, but that's just not the case.