The choice here is between having a few different types of missiles that perform well in certain roles against different types of targets, and having a generic one size fits all missile.
There is also the option of having a few types of generic missiles to fit certain conditions (like range).
The first thing I wrote was that you can design missiles against generic target types without knowing anything about your enemy ( or even having met them ).
Newer players can't really do that as they don't really expect what kin of things they may go against before they do.
If you have to use them against the "wrong" target they will not be performing worse then a compromise "one size fits all" design will, which also is not tailored against the target.
This is highly circumstantial. Sometimes using a specialized missile against the "wrong" target has the same effectiveness as a generic. Other times it is worse off. It depends on the specialized missile, the generic missile, and the enemy that it is hitting.
They will however perform better when they are used against their intended target, so there is no downside to the approach.
A misrepresentation using the "because there is an upside, there is no downside" way of thinking.
1) catch the target, and 2) hit it. Clearly, the 2 conditions are fairly tightly bound, because both speed and AG contribute to final to-hit %age, but only speed contributes to condition 1).
Not necessarily. While that is true against enemies headed in the opposite direction, it does not apply to enemies headed directly at you or sitting still. I've had plenty of cases in my own games where I have been hit by surprise missiles that were slower than my ships, and where I've hit enemies who were faster than my missiles.
Having a high to-hit value is worthless if your ASM cannot in fact catch an intended target, thus one of the design considerations is how to allocate MSPs to maximise your ability to catch and hit a target of unknown performance and specs.
Just because you sacrifise some MSP % from engines and put it into agility, does not mean it will not catch the enemy. Your argument seems to be based on sacrificing most of your engines to put into agility.
Therefore, one approach to ASM design is to maximise your speed. As we know, both speed and AG factor into the final to-hit calc though, so it seems likely that allocating some MSPs to AG will lead to better overall ASM performance. All missiles start with a base AG of 10. If we choose to allocate enough MSPs to increase that to 20, for instance, we use an amount of MSPs to double the AG stat and thus improve the to-hit value with a method independent of speed, but is there a better choice?
Another factor is retargeting when the designated target is taken out, so you want onbord sensors which sacrifice either warhead or engines/fuel. Another factor is making sure the enemy can't hit your missiles, so that is space into missile ECM. If it does get hit, you don't want it to die so you need to armor it. You see where this is going? It isn't about 1 is the best, its about tradeoffs. While having a generic missile is a very good idea, it lacks the specialized performance these other types of missiles get.
Every subsequent commitment of the same amount of MSPs suffers from the law of diminishing returns, decreasing the benefit we gain overall. Going from 11 to 12 only nets us a gain of about 9%, rather than the 10% we got the first time, and so on until the increase from 19 to 20 is only gaining us ~5%, about half the benefit of that first commitment. Thus, setting AG to 11 is an "optimal" design choice, because it gains us the highest possible increase in overall to-hit, for the lowest investment of MSPs..
Engines also suffer from diminishing returns while you don't see it unless you go crazy at mid level techs, as you start advancing into really powerful engines, you notice it quite a lot. It gets to the point where even the "optimal" percentage of engine to missile starts becoming sub-optimal compared to other designs.
Ideally, yes. If the first time you meet a given race is when their war fleet drops into Sol or a system one jump away or something, you might want some ordnance on hand though. So having some missiles would be better than having none. And having missiles that are more likely to be at least somewhat effective is generally better than having missiles specifically designed for the wrong target
However, you can also design differing generic types of ASMs, like Long range that sacrifices speed/warhead for a bit more fuel, or short range that sacrifices its fuel for more speed/warhead. Etc. There is more than one type of "generic missile". My generic ASMs always have some onbord sensors so they can retarget while inflight as to not waste resources.