10 seconds is just an example. I really don't see how it's ridiculous. Under 10 seconds your healing skill would have already cooled down and you could have another chance to heal/damage. Assists also grant gold, so they can't just be handed out. Bottle sharing, health/mana freebies, and stuff like Chen global heals would qualify under your ideal assist rule. How about passive regen auras? Should any allied hero that gets a kill under your aura credit you with an assist? At least mekansm is activated. I guess we have a different notion of assists. I really think DOTA's assists are closer to how sports like basketball would classify them (kill=goal made). It might seem primitive to rely on just damage, applied effects on the enemy hero, and general proximity to be the only indicators for an assist but opening up the criteria might really just raise more questions than provide answers. DOTA's been like this for years, with some slight tweaks every now and then to accomodate slows and global ults. Maybe it will change, and if your opinion is shared by a large enough player population then perhaps Valve will take notice. As it is, with the current game design and metagame, I (just me) believe assists are handled well enough.