Gyms are too easy to take over

I'm not asking to make them near impossible, but I'd like it to be a bit more balanced. If I'm there defending my base and I'm a higher level, then I should be able to prestige it as much as they're taking away. However, that's not the case.

It'd also be cool if the game gave you a notification that your gym is under attack so you can go try to defend it. Now if there's multiple people there taking it you shouldn't be able to defend it just yourself, but those other guys will get notifications too and could come to aid you

Edit: my team has gotten multiple level 10 gyms and they never last more than an hour, but take nearly an hour just to prestige it that far. I'm the lowest level at 20