So then I should stop trying to cap or hold flags on my own when playing as Regulus, right?
The thing is it seems natural to do that because if I don't go to that flag right away, then no one else will since my allies are already busy capping other flags. Therefore it seems like a tradeoff in that the enemy can get more flags capped initially.
On the other hand, being alone as I cap or try to hold flags causes all the other problems mentioned.
I guess the tradeoff is just something I have to accept, and stick with an allied DG at all times to cap and hold even if it means we have one less guy (me) capping individually and therefore we get less flags due to that?
My Regulus can stand alone against other DG's only early in the game. That's when I'll be getting our first flag caps in while grinding mobs to get my first couple of level and harassing other enemies players out of my lane.
In early-mid game, however, I will absolutely need support to at all harass the enemy and cap flags. After I have levelled up my mines, I will be able to seed areas well enough to hold of the enemy for short periods of time. But even then I can only do that temporarily if there isn't a strong bottleneck, which few maps have.
And no, it should not be a "trade off," as you put it, since if you and a another player team up together to push back all your enemies that are trying to solo, they will not be able to stand up to you, and you can confront them, quickly force them back, and cap/re-cap your flags.
So if your enemies are foolish enough to try to solo everything, and you know how to play as a team, you should not be getting less flags: you should be getting more flags. In games I have won, I do frequently get the highest number of flags capped.