Auto Blitz and Blitz Beat are a bit different in terms of mechanics (number of hits and damage divided by number of enemies iirc, and yeah, no delay). Though Auto Blitz share with Autospell procs the ability to proc on misses, which is one of the main differences of Autospell and any autocasting stuff triggered by items. But yeah, Auto Blitz triggers no ACD, item autocasting triggers no ACD, Autospell procs do trigger it. When normally attacking and casting a skill (like some selfbuff for ex, as you suggested), you stop attacking and cast it, click again - you continue autoattack, same as before. Bolt ACD is big, you wont be able to cast anything with 190ASPD unless you're staying in bragi :D. Still, for me it's not that odd to expect from it some special behaviour. IRO Wiki Classic has this note:
"Skills triggered by hindsight do not have any cast time, but do have cast delay. Cast delays, however, will not prevent bolts from being triggered via hindsight. As a result, it is possible to fire off bolts very quickly. The skills will all retain their special effects on their targets; Frost Diver will freeze, Fire Ball will have splash damage, etc."
I know there are differences in skill mechanics in iRO and kRO sometimes, and afaik we tend to be closer to former. Still I yet to see any video or hear from anyone who played there if our current skill mechanic is the same as there. Basically, what Boreas said in Bug Report post. So most likely we won't see any change on this part, unless rAthena way is different from iRO way and it is the actual rAthena way, not just a bug. What we might suggest, and what is more likely to happen, is something of "add matk% to Tome's item description; add new SQI bonus - proc Health Conversion on hit or disable/lower Autospell procs ACD or whatever", with upcoming SQI revamp.
Storm Gust was there just because in pre-Iduna HW could easily and with basic gear solo kill a lot of stuff. New mechanics are that monsters aren't staggered that much by SG anymore. Necros aren't sleepwalk anymore, Thor requires patience, etc, I'm still curious to try GQS and Mammoth. So people complain everywhere 'meh, nerfed HW' (it's also about JT rate and overall damage but still), while I find these 'nerfs' just interesting and challenging.
P.S. Good like with making client to work, Sachi