I'm going to leave this here so you know what kind of experience I'm basing my comments on. I've seen you in these forums a lot giving advice on what players are doing wrong, while really never holding the mechanics of the game accountable. Just a bit of a resume so you know that I have some semblance of what I'm talking about.

Cool. Now, you're not wrong by saying playing conservative in 3's is the best way to prevent OPs gripe. Always playing with a bot D is a precarious choice, but when you have a game as inconsistent and as low pop as EA NHL, you can't always afford to not play games with a bot (I hate calling them AI because there's no intelligence to them).
I think OP would've been fine with a 3v1 against because, as forwards, they've got to try to push the offense. All he's saying is that the bot should be able to cover the rush all the way back to the goalie. He doesn't have to stick check, hit, or make a play to take him OUT of the play, but just be a bit of a menace to make the forward do something besides straight line to the goal. If the bot is not going to contribute to the offense and is camping the blue line while the puck is in deep, he should either be able to skate backwards and stay between the puck carrier and the goalie or turn at the appropriate time to match speed and make a play. Getting blown by without any hustle while not making any attempt at being a D-man is behavior that EA needs to address and haven't for as long as I can remember.
In older NHL games I was primarily a 3's player, but transitioned the last two years to 5's and 6's. Bot D's are generally avoided by skilled players (wink) for the reason I just outlined. If I'm playing D with a bot I know that I have to cover the bot's assignment and my own assignment on the rush because in 5s and 6s, players are going to skate the same.. exact.. way.. against.. a.. bot.. and... blow.. by.. it. It almost never fails. It's also very difficult because if you start trying to play D for the bot and yourself, it makes the bot go defensively off the rails. You can repeat this same scenario in any of the MP modes. You can play the offense coming at you perfectly and still have to compensate for the bot (In OP case, it means playing as a D-man and not a forward). There are instances where people say they have played against amazing bots, and that's because the bot seems to be able to easily take the puck from you in close quarters, shove you off the puck easier, and regain position of the puck easier if there's a battle. Passes are sometimes intercepted or broken up easier than if a human was in the same spot. Some bot defense will also jump into the offense and aggressively play this way and you'll usually hear in party chat, "What is the bot doing?!". Truthfully, no one knows.
All I'm saying is that OP knows it's going to be an odd man rush against him. He knows he and his partner will have to play a bit aggressive because there isn't a human D to contribute to the offense that knows how to use the hustle mechanic. He knows he could've played more conservative. Duh, right? His gripe is that if the bot is just slightly more competent in keeping up with human players with perks that EA keeps throwing at players, and not a HUT bot skating in sand, then it'll be an easier pill to swallow. I'd certainly like the same for bot D in 5's and 6's.
It's fine to critique players as this is a public forum, but please don't handwave the mechanics of the game like it's perfect and we shouldn't fight to pressure EA to create better mechanics. Especially the BOT mechanics.