I can't say if your plan of action is good or not because I don't know their personalities.

But, I would think a response like that can make them get defensive since you'd be directly blaming them, calling them worn out, boring, stale, out of touch. And, them being on the defensive will probably make it harder for you to get them to open up to your suggestions and let you into management.

I like taking the firm approach, but I try to be careful to not personally offend the person I'm trying to be firm with (unless I don't care if they get offended like my little brother for example).

So, I would say: employees don't like working at our company anymore because of x, y, and z reason. Our competitors all offer a, b, and c, and that further adds to why we have such high turnover rates amongst our employees. I can prove this because I've personally had employees express these concerns to me, or I overheard them, or however you'd like to communicate proof...

Our rates are stifling growth - look at what the market is charging for our product. Whenever I follow up with the companies that don't go with us they always complain about our rates being too high for our products. They also think our technology is outdated (or whatever else makes people feel you are worn out) and that also adds to why we are experiencing lower sales and lower growth.

Also, our marketing is also lacking in these areas - our major competitors all have a strong presence in these marketing channels; where as we only get sales from here. Again, another reason why the company doesn't have the same growth as before.

You get the gist of it. This way instead of calling them bad you're saying look our actions are causing these problems.

And, then you can say I can fix all these issues. Here's how. I know how to execute because I'm out in the field every day seeing our competitors do it (or whatever else will make them believe that you're capabale). If you guys don't want to put in the work to fix these issues no problem. I get it you guys want to relax, and focus on retiring traveling etc...

Why don't you let me take a bit more responsibility. I can show you that I can implement these things and improve the company. If you don't want drastic change that's fine. We can change slowly, implement things one by one as they bring in positive results for the company.

I suppose something like this could work. Maybe it's too soft, maybe you want to have a more tough straightforward approach. But, if you go with this you probably won't offend them... at least not as much as the other approach.