correction: spiders are faster than lynx. I know becuase I constantly have to stop them to wait for the emp lynx (even with speed upgraded) to catch up.
Is this happening on black rock tiles? Arachnids aren't slowed down as much due to terrain, though they still have a lower base speed than upgraded lynx.
The fact is, in Multiplayer, if it were possible to forcefully limit the amount of space ports allowed, then it would make it even.
Not sure if that'd be the best way to go about it. Nerfing the resource cost, build time, and/or landing delay would probably be best. There is still the other factor that EMP missiles don't count towards your unit limit, so once you hit it you might as well put the extra resources into missiles.
As for spiders and scorpions, they obviously need to be fixed, but it comes down to a point "do they really need to be in the game at all?".
Don't think they can really be fixed without some major engine hacking (most likely too major to be feasible). There's two things, besides their lack of hitpoints, herp derping (spiders), and weak weaponry (scorpions), that makes them undesirable. First, all units occupy the same space (1x1 tiles). Because of this, and how arachnids are designed to be massed to be effective, they have problems swarming through bottlenecks; they would work more nicely if they occupied 0.5x0.5 tiles, but that would for sure require TONS of modifications to the engine; at that rate, you'd almost be better off just rewriting the game. Second, all units count equally toward your unit limit, as opposed to, for example, Starcraft where different units have different "food" costs. You simply don't want 30 scorpions eating into your unit limit when those could be 30 RPG or ESG units.