Gyms can't be held for very long, in any scenario other than remote destinations that nobody visits (like a reef 2 miles from the coast or a desert monument). 3 Perfect Pokemon of the highest tier will be burned down by 6 Pokemon of various quality (multiple people using 6 at a time), especially with the rock-paper-scissors counters available.
That's been my experience too, taking gyms is considerably easier than successfully holding them for any length of time.
That said, you only really need to hold it long enough to claim your coins, and the XP for fighting rival gyms is probably more valuable in the long run.
