Archery should NOT have 100% aim, but at the same time, having it on pure RNG base is an issue, at least from my view.
So, I would suggest two; feel free to offer thoughts
1) Random distribution rule.
The uniform or true random distribution describes the probability of random event that underlies no manipulation of the chance depending on earlier outcomes. This means that every "roll" operates independently.
The pseudo-random distribution (often shortened to PRD) in Dota 2 refers to a statistical mechanic of how certain probability-based items and abilities work. In this implementation the event's chance increases every time it does not occur, but is lower in the first place as compensation. This results in the effects occurring more consistently.
The probability of an effect to occur (or proc) on the Nth test since the last successful proc is given by P(N) = C × N. For each instance which could trigger the effect but does not, the PRD augments the probability of the effect happening for the next instance by a constant C. This constant, which is also the initial probability, is lower than the listed probability of the effect it is shadowing. Once the effect occurs, the counter is reset.
https://dota2.gamepedia.com/Random_distribution
Example (borrowed from dota 2 wiki)
Slardar's Bash of the Bash of the Deep has a 25% chance to stun the target. On the first attack, however, it only has an ~8.5% probability to bash. Each subsequent attack without a bash increases the probability by ~8.5%. So on the second attack, the chance is ~17%, on the third it is ~25.5%, etc. After a bash occurs, the probability resets to ~8.5% for the next attack. These probabilities average out so that, over a moderate period of time, Bash of the Deep procs nearly 25% of the time.
Following this logic, lets set up a commonly agreed rate for archery (85%, for an instance? or make this value to be dependent on your DEX?)
So more you miss, more likely you will hit next time, eventhough there is a chance of missing. And chance is back to the agreed rate if you land a hit.
2) Let aim infleunce damage, rather than accurancy per se (if it ever does hah)
Combined with first rule, it should lessen the problem perhaps?