Our board is four by seven for games larger than 2000 points Moving up to six by eight for really big games. Bear in mind that a single unit of 10 workers can completely cover a 12" diameter circle and can then move up to 18" with coordinate. It's entirely possible to negate that mobility, it just takes a lot of forward planning. Also, that unit is only worth 100 points.
The point of playing the game is to come up with something that alters the balance in your favour, (be it tactical, strategic or a one shot trick that nver works again).
E.g. with 3000 worth of workers you can cover the board with a tunnel network he can't get away from....... so he needs to alter his tactics to fit, taking out tunnel assets etc.....
That's what wargaming is about, move and counter move. If he can't rely on jumping out of the way of close combat, then he has to think of something else.
The biggest problem facing a bug player is the mobility of the MI, you need to counter that (using hoppers to outrun them being the classic tactic). I tried saturating the board with low cost troops (10 points each), I was playing an opponent who was sure I'd use plasma bugs, tankers etc... and had geared up accordingly. He was left trying to take out 200 workers with nukes etc... he'd bought to go for the big stuff. I lsot nearly 60 bugs on the way in...... but there was enough left.
He needed to modify his tactics, now his armies are more balanced as I might just do that again

Having all of those warriors available stops an MI player from looking at your collection and knowing what he'll be facing, if he sees you've got 60 warriors a tanker and a plasma bug on your shelf , he knows what you've got in your army as the bugs just don't have that many surpises in the form of upgrades.
Main thing when writing a bug army is to keep him on his toes, if he knows you are going to have just warriors, then he'll flamer up. If he knows you have tankers then he'll up the javelins.
You need to make sure he is forced to remain flexible. If he has to think about plasmas, tankers, warriors, hoppers etc.... then that means he has to balance his force, if he knows you don't have any plasma then he doesn't have to field anything to cope with it.
If you are playing a 2000 point game and have enough warriors that you don't have to field you tanker, then he has to plan to take out a tanker or a huge horde of warriors...... either way he'll 'waste' some points as he'll have to take a weapon that won't be optimal in one situation. Force him into it.
As a bug player, you really have to make sure that your opponent can't work out exactly what you'll field, not having to have a balanced army is a massive advantage. IMaigne how much easier it is to plan an army when you know what the other side will have? With MI they can all go capsule without needing new models, traits, frag grenades, trenchsweepers plus weapon upgrades are cheap to do and fleet assets are bits of cardboard.
And who said removing the mobile form MI wasn't a problem? I didn't, it's the biggest challenge you've got, but it's achievable.