Okay, but your first point seems to disregard the escalated importance of backing up and completing runs in t20 cricket. It could be argued that there is more importance in the batsmen backing up as much as possible so that those vital runs can be completed, and hence the possibility of ending up marginally out of the crease by the time of the bowlers release is increased.
And this is certainly comparable to where a bowler is taken through the wicket and the way that they must coordinate themselves so as not to do it. A batsmen must be treading the fine line between backing up well and too well so that they could potentially be run out. To not be doing this afterall, would be against the very premise of attempting to score runs as quick as possible
Hence, I reckon a warning and nothing more for the first offence is justified, and a dismissal should only be attempted if this warning has subsequently been ignored. It would be extremely negative for the game if bowlers were to have to be in constant fear of running across the middle of the wicket in case they were instantly taken out of the attack, and this is why warnings make it better. The warning for mankading is really the same principle.
Any argument that, "... cos T20 ... blah blah blah," clearly has not been thought through in terms of actual cricket. By this argument, let's add a 5-second period in which no run-outs can be made because runs are at a premium so that things should be made easier for them to be able to complete them. Let's remove the short-run rule because that little extra bit of thinking about where they put their bat could cost them that second tight run.
What does 'scoring runs as quickly as possible' have to do with anything to do with the laws? Where do the laws stipulate that, "play should be conducted so to allow for the quickest possible scoring of runs"?
Why does it matter that it increases the risk? How about we remove such run-outs entirely then: the bowler cannot run the non-striker out before he releases, not before he begins the swing of his arm, not before he enters his delivery stride, not ever. That'll definitely cut down the risk they face.
Furthermore, it is a very batsmen-centred argument, and one that has no justification beyond, 'make things easier for batsmen to do x.'
Or, we can accept the rules as they are and batsmen can deal with it. They'll have to score runs as quickly as possible whilst following the laws.
Furthermore, it is not comparable to a bowler running on the wicket. It is most comparable to a batsman running on the wicket: both actions involve running towards the other end of the pitch, and so carry some possibility of running on the pitch. In both cases, there are options open to reduce its possibility, moer for the batsman because he is not required to stand inside the return crease and can so be further away from the protected area. A bowler has to stay within the creases while bowling and because he will have more momentum going forwards (whereas a batsman goes from close to a standing start), particularly if he is fast, that increases the possibility of running on the wicket, and it is harder to control be virtue of simple physics. Until we invent a bowler who can follow through at a right angle immediately after bowling, it keeps being a possibility. But, the physical nature of bowling means that a bowler will necesarily take at least one step beyond the crease [possible exeptional exceptions aside].
By contrast, a batsman can start his run at any time. He could wait 5 seconds after the ball has been hit and only then begin to run. The act of backing up or running
does not necessitate leaving the crease before the bowler has released the ball. He is not already moving in the same way a bowler is.