Well what I mean is that the entire roaming legendary mechanic sucks major because then you begin the event you can spend almost an entire day trying to catch the thing, but because of the fact you have no idea where it'll turn up before it is first recorded in the pokedex, it leaves you with no safe way to actually set yourself up for the hunt. Diamond, Pearl, and Platinum moved a step in the right direction by not limiting the tracking of roamers to the pokedex only, but the problem of getting the right one for competitive battle use was another considering legendary pokemon can't be bred.
The guys at gamefreak seriously screwed up on how the roamers worked in platinum and JG/SS by having multiple roaming pokemon at once, because even if one used the synchronize trick to influence a decent nature on them it has a good chance of failing. I mean I get part of the challenge is stuff about pokemon is randomized, mainly to allow for multiple strategies for different individuals of the same pokemon but some pokemon have extremely limited usability, even with the newer advancements the series has made since gen 3, and as such being forced to rely on luck that much for a valuable pokemon you have a very low probability of catching anyway ends up making it more trouble than its worth.
Now since you mentioned an IV glitch was corrected regarding the roaming legendaries in this that alleviates one concern. Legendary pokemon are supposed to have very strong IVs, however random they may be, so with a bit of luck getting a decent hidden power attack isn't too hard.
The biggest problem I have with roamers though is the natures, as its one thing to get good IVs, but another to get a decent nature if not the perfect nature on ANY pokemon. And hidden power is determined both by nature and IVs of a specific pokemon since generation 3. For example on an Entei, I like to run a Modest nature so I can work a passable special sweeper using Hidden Power Grass along with Flamethrower or Fire Blast as its main attack, and with Entei's base special attack otherwise being lower in strength to some of it's other stats I have to make due somehow. If not with modest either mild, hasty, naive, or rash also works since its stats are perfect to allow a mixed set where applicable. The problem however is actually FINDING this hypothetical entei first since if one saved AFTER starting the event that activates entei then you're stuck with a potentially crap nature no matter what you do, and given how Fire Red treated this originally, considering you made this hack to start with the national pokedex that sorta ends up making me question how that entire event plays through.
I hope this explains what I mean, though I know there's little to no chance of you wanting to fix it, you said you were done with the hack entirely as of the last update. As such I wont expect you to do anything about it, besides this game is pretty good regardless. Its just the roaming legendary mechanic just REALLY REALLY grinds my gears because it makes it next to impossible to really do anything with said legendaries. I really like how X/Y handled the roaming legendary birds, a far better method as they flee before you sent in your pokemon to battle, then flew to a fixed location for you to catch them that allowed you to "choose" what nature you desired like other non-roaming legendaries.