I don't realy think slime is underpowered, you just have to make a choice between using slime or making some good virus defences and hoping for the best. In the end if you can cut a resource you'll have more nrg, so it will always be an imporvement if you no longer need slime in your bot. And some bots do make enough slime to keep oponents out, I think Conquistador just has enough slime to avoid getting infected and I remember I had problems getting past it with Ebola because it relied on the virus to kill the oponents but the virus never managed to infect it, even though the virus in ebola fills up the field with well powered virus shots rather fast...
But viruses aren't realy an issue ATM... I can't think of a reason to use a virus when I can rape instead. With raping there's no charge time, no added costs, I can aim and infect my target, takes loads of poison if people want to stop the memmory shots, I can also transfer as many genes as I like of any size. Granted you need to get closer to infect someone, but once you infected an oponent you can just relax and let the infected oponent do the rest of the work, you're not inserting a small infection, you're taking over and inserting a large complex behavior.
And I used Mulitply4, and I'm aware it's weak against mutations but it was mostly to illustrate the point that some bots are much stronger against mutations and should alteast get some credit for that.
Also the broken ebola wasn't firing it's virus, but with mmutations the virus became active about 20% of the time, so there was definately improvements through the fight.
I realize you won't see any ground breaking evolution this way, but you will see good examples of single mutations having a very benefitial effect on it's host.
But mainly the point would be to weed out bots with defences that only work with no mutations and conspecs that break down too fast and other such stuff...
The higher the mutation rates the more emphasis would be on mutation resistant bots and less on evolution, and that may be the best aproach since evolution isn't very likely in bots unless they're broken or buggy copy paste monsters and such... (I'm pretty sure noone wants to run very very long fights in a huge field, and evolutions usualy takes some time)
But evolution CAN happen, even with very strong handcrafted bots in environments with heavy mutations. Often a small tweek can make a huge difference, using more shell, or less poison, or having more or less speed, and stuff like that. Problem is ofcourse that high mutations will tend to break down everything, even the bots that where evolving... and lower mutations may not realy take effect before the fight is over. So I wouldn't hope for too much evolution... rather focus on a league for bots that are hard to break down. Not even sure it's a great idea or anything, but just seemed like the stronger handcrafted bots are always weak against mutations. People are always asking for mutation resistant conspecs and such, but I have yet to see a hand crafted conspec that can compare to the ways evolved bots handle it. (I do have an idea on how to create a much stronger conspec that should prevent the evolution of canibots, largely inspired by the behavior of the bots in a sim I was running)