My 5 sec : 5 min power ratio is around 4.45. But a 50th percentile rider according to this chart would be around 2.66. Which means it’s way easier for me to hit my max HR than a typical rider. I suspect you’d have a much lower 5sec:5min ratio.
More here:
https://www.cyclinganalytics.com/blo...output-compare
Very fit runners will find it difficult to max out their HR on the bike. It’s not as demanding. Your max HR is very personal and is best determined by running on an incline treadmill.