Your development model is similar to the famous "survivorship bias" chart, in that your monetary feedback only reflects the customers you have, not the ones who delete the app after 5 minutes. What you see in this thread is some people whose feedback you would otherwise be missing.
What you do with that knowledge is up to you. Perhaps the educational market it something you want to attract as potential new customers, perhaps it is not. I can't tell you. I am just saying that telling people who have already told you they simply can't use the app because it is missing a crucial feature that they should pay for it is a bit counterproductive. If you want the support of these users you need to make them into users first. Maybe doing so isn't worth it, maybe it is - that's a judgement call.
A secondary issue is how a user who normally would have just deleted the app but takes an extra few minutes to find the forums, register an account, and report a problem might feel about being told that if they really want something they should pay for it. That might be true - if that is your model - but perhaps there are ways of responding that would be less likely to put people off? Personally I don't plan to spend any more time on this and will be muting my account.
