I wasn't sure how to count technical free throws. Someone like Ray deserves credit for the difference between his shooting and the average FT% of shooters of technical free throws, but I'm not sure I would work that into the efficiency due to complexity. Perhaps it is better to not try to include everything?
I think the clear path fouls need to be accounted for since it is only certain types of players who will get them. Perk or Shaq, for example, will not get clear path fouls. When Rondo misses both shots on a clear path foul that another player would not have been fast enough to generate (by getting ahead of the defender or getting a steal), I wouldn't count that against him using the .44.
Ray does get credit, when he makes technical free throws that improves his TS%. If he misses them he's still costs the Celtics a chance to score a point isn't he? Why would you need to differentiate from a normal free throw?
I don't think there are enough clear path fouls. Rondo took 282 free throws, how many would be from clear path fouls? And again regardless of the source of the free throws missing them still costs the team points.
If the stat is being used used to measure scoring efficiency, costing the team points isn't enough to make it into my denominator.
Like I have already mentioned, if Rondo scores and gets an and-1 which he misses, it did not cost the team points. That possession ended with 2 points, which is well above the league average for points per possession. We could say that every time a player scores 2 points he costs a team points because he didn't shoot a three, but that seems quite bizarre.
If we are going to capture tech FTs, it is not clear to me that the previously mentioned multiplier of .44 still makes sense since it isn't clear how to relate FTAs to possessions and since not all players need to be selected to shoot techs since there are multiple good FT shooters on a typical team. I mention this because Paul Pierce is good enough from the line that he was worthy of getting more free points from techs. The main reason he didn't is because he plays with Ray Allen. Yet if Pierce took the shots, he would have benefited statistically.
I'll put this in terms that relate back to your comment: shooting 65% on Tech FTs costs the team more than shooting 65% on FTs after a missed shot since the league average for points per possession is considerably lower than the league average for points per 2 technical FTs. Missing 2 FTs after a shooting foul cost the team a little over one point. Missing 2 FTs that were both a result of a tech probably costs the team over 1.5 points.
I'd have to construct a study on this issue before I'd declare it a problem or not.
I think a factor of .44 accounts for the average number of possessions a person who takes free throws. The average number of technical free throws, and-1s, and clear path fouls for any individual player shouldn't skew the results that much.
I think TS% is still a better measure than points per shot, eFG%, and FG% if you're looking at one measure.
If you want to remove this factor than you can multiply eFG% out to get points per shot without free throws. You can then look at Free throw rate and other measures.
But for one statistic the issues you raise aren't large enough for me to even blink when using true shooting. Especially when the .44 factor already addresses the fact that a free throw is less than half a possession on average.
http://msn.foxsports.com/nba/sortableStatsTeam?league=NBA&stat=technicalFoulsPlayer&table=fouls&dir=descendingLook at how few technical fouls there are, for the Celtics a team who fouled a lot and led the league in technicals. (both team and player techs) There are 100 technical fouls and the Celtics opponents shot 2152 free throws. Technicals are 4.6% of free throws attempted.