I never had much of a problem with Essentials classes because in effect they fit right in with the more complex classes with mostly no issues. My son, for example, prefers the Slayer to the Fighter specifically because of the simplicity and being able to effectively switch from melee to range. Should they have fixed the math at Essentials time? Probably, but then you would have had some incompatibility within printed product lines and a lot more nerdrage. The math fixes you mention are exactly what we implemented and had no issue with leaving the feats if someone wanted to further have better accuracy. The core of 4e is very robust and a bonus here and there are not really going to "break" the system.
The main issue with the OP is that you really don't need an OGL, at all, to clone 4e. Game mechanics themselves are not copyrightable and anyone with the time, inclination and effort could put out a system completely compatible with 4e. But that is the issue you have to spend the time, and effort to not infringe on those things that actually are copyright. Most people that want to go the clone route simply want to copy verbatim from document A and paste to document B and call it a day. You can absolutely do that for personal use, but can't do at all in any form for distribution.