Agreed he's very good, but what film could have been his Oscar?
The Fugitive?
Bladerunner?
Indiana Jones, Raiders of the Lost Ark?
No.
No.
No.
He has made many entertaining movies and will likely win a honorary Oscar, but he has not turned in a Best Performance by an Actor in a Leading Role to rival any winner. His one nomination was for Witness. Samuel Jackson has had a similar career: entertaining films that made a ton of money (more than Harrison Ford films), but his one nomination was for Pulp Fiction. Neither Jackson nor Ford are in the first tier of actors.
Director intentions aside, Blade Runner does not make a credible case for Deckard as a replicant.