most total annihilation units couldn't shoot past each other, the one who could where large, slow, fragile or otherwise unable t effectively blob due high weapon spread or vulnerability to splash damage.
my favourite highly blobbable unit for fooling around in single player was advanced construction aircraft. i guess if you've got enough resource income to support 20+ advanced construction aircraft rush building lines of long-range artillery, you've probably already won.
Hardly. My group had glorious 4v4 games where getting your swarm of 500 advanced construction aircraft to build vulcans and buzzsaws that would maybe get off a few shots before being destroyed by your opponents' counterparts was the name of the game.
In fact I remember my first internet game (after playing with friends for some time); noone even rushed me, and I had a chance to get to L2, expand as I always did and build a couple dozen Mavericks for my would-be attack. Then 10000 L1 missile vehicles rolled in and blew everything up.
EDIT: and one of my most epic games, a 3vs3 on a 3-bridge map with aircraft and navies disabled, actually involved blobbing nukes. The lone player on the "losing" side was able to hold me and the other "winning" survivor off behind batteries of artillery and infinite piles of wreckage for long enough to find our commanders and send enough nukes to overwhelm anti-nuclear.