Totally disagree. Whether you find him interesting or not is a matter if opinion I guess, but even among the characters on Deep Space Nine, the growth over the course of the show of Bashir - a character who on first impressions has no obvious baggage, unlike Sisko, Kira or Odo - is quite dramatic. In seven seasons he goes from idealistic, enthusiastic to a fault albeit somewhat inept socially and professionally to cynical and rather jaded but accomplished professionally and personally. In short, I think the character was handled exceedingly well by the writers.
Well, it certainly is a matter of opinion, and I'm glad you found the character interesting

One problem here of course is the revelation in the middle of the run that the character up to that point had been something of a fraud. You have to wonder how inept he really was given that he was downplaying his abilities to avoid being seen as superhuman, and how idealistic he was given that he was systematically deceiving everyone.
This is a retcon of the character of course, but you do have to account for it when discussing the arc of the character over seven seasons. This in itself might have been interesting if it had been delved into, but the writers seem to have chosen the path of least resistance on this one. Fortunately, they didn't do this often on DS9.
And friends (as well as lovers, siblings, co-workers, etc) lie to each other all time, I don't think for a second his 'mutant' revelation would prompt the dissolution of Bashir's friendship with O'Brien, it was shown time and again to be much more solid than that.
Certainly, friends and lovers lie to each other. Some of those lies may be white lies, and others may never be revealed. However, the revelation of lies and deceit can be a serious threat to any relationship built on trust.
In this case, we are not talking about a single lie, but a constant stream of them. This is especially true because Bashir and O'Brian's relationship was a partly competitive one. And then O'Brian finds out that Bashir has been intentionally downplaying his abilities. Basically O'Brian (and everyone else) learns that Bashir is an entirely different person than they thought, and yet they seem to have no reaction

That doesn't mean that the friendship might not have survived. But it really needed to be addressed more directly than it ever was. There was a bit of tension during the final arc which gave a hint of how this change might have affected their friendship, but I think there needed to be more.