I think it's all a matter of personal preference and situational circumstance.
I've been fortunate enough to never have had to buy a set of irons as of yet. The only clubs I've purchased have been my R9 driver, R11 3W and White Ice putter.
The reason for that is my dad, who has a 5 handicap, always gave me his old clubs when he upgraded. The fist hand me down set were some Accuform II's which, if my memory serves me right, were cavity backs. I played those for a around 5 years, 5-10 times a season.
Then I got the Mizuno T-Zoid Pro II which are a muscle back. I was hitting the ball much better and my swing was more consistent with the Accuforms but I was in for a wake up call. I noticed a big difference in my game as it took me a while to learn to hit these clubs properly. My swing had to improve and once it did my game as a whole got more consistent, especially achieving good contact. I was able to figure out what I did wrong because of the lack of forgiveness in comparison to the Cavity backs. I was still playing around 10-15 times a season.
Then last year my dad upgraded once again and he gave me some Mizuno MP-32's which again gave a bit of a wake up call. One little mistake and you see it. I like that though as it proves to be a solid challenge and got me hooked enough that I'm getting my first membership so I can get to the next level. My handicap is currently at 17.5 and my goal is to bring down to somewhere around 10 and hope to break out of the 80's for the first time.
I don't think I could have gotten to where I am today by hitting forgiving clubs as with blades it lets you know right away when your doing something wrong and forces you to correct it.
I guess it's to each their own but I feel it can help your game more than hinder it. I think that it was all part of my dads master plan for my golf game lol.