Yes, the bolt and carrier get hot (in this case the cutout is in the bolt carrier). The exhaust vent for the gas impingement operating system is in this slot as well. A handful of shots will get it too hot to touch with an unprotected finger.
There is no material benefit of not having a forward assist. You will not walk further, hunt longer, shoot straighter, reduce risk, increase reliability, clean faster, fight harder or defend better without a forward assist. As I mentioned in my first post on the subject, I have never been in any situation in which I have thought “this forward assist is limiting me.” If you, simply by preference, want a cleaner, smoother sided AR15, then there are options for that. Further more, for the average recreational user of an AR15, the absence of the forward assist also introduces nearly zero material risk. For a recreational user of an AR15, it is strictly a preference to have or have not, a forward assist. It’s no different than wanting ambidextrous controls, an extended magazine release, specialized trigger or any other ergonomic or esthetic preference.
For someone who’s using for defense or offense, deleting the forward assist just eliminates one more option in a critical situation. In those situations, as the cliche goes “better to have and not need than need and not have.”
The question better asked is: for what you depend on an AR15 for, does the preference for the esthetics of no forward assist outweigh the risk of having on less option in a critical situation? Only you can answer that.
A couple questions:
First, does the bolt get hot? I seem to remember grease guns had cutouts to retract the bolts on the later models, and always wondered about this on them as well.
Second, is there any downside to having a forward assist? I generally prefer simpler setups, and actually thought the original charging handle on the XM-15 original Armalite AR-15 was a good idea, though it of course didn't allow for a flat top.