We have never been on the WDW marathon weekend but have been there for Wine and Dine and to be honest we had no idea it was going on until it was over and we seen somebody with a bag. After that we have been down there for the Princess Marathon weekend, Tower of Terror 10 mile weekend, and Star Wars Dark Side weekend and ran in the 5-10k events and never had an issue with park traffic even on the 1/2 marathon days. I know the WDW Marathon started at 5:30am (the last corral should have been through by 6:15 at the latest) to minimize any inconvenience to park guests.
I know that at every entrance to the hotel they have menu boards telling you about the races (pick up time and schedules). Should they have done a better job at the front desk letting you know to adjust your schedule, maybe. Should they include something in the check-in paperwork, probably.
What I do know, as somebody who has ran in the events in and around the parks and resorts, it is absolutely AWESOME when random park guests stop to cheer you on and give you high fives as you run through. Instead of complaining about them, take a few minutes and cheer them on! These people are running anywhere from 6.2 miles to 26.2 miles and some of them are finishing up a 48.6 mile challenge, give them a little respect.
As for making rope drop, the OP never said when he left the hotel or what hotel he was at. If you staying Moderate it can take 15 minutes to get around the resort depending on your stop. With it being the last rope drop I would expect everybody wanting to be there and resort bus and park entry lines to be HUGE!! Typically if we need to be somewhere at a specific time we leave 1 to 1 1/2 hours before we need to be there. I know for dining reservations Disney recommends leaving 1 1/2 before your reservation time.