The following is the 2021-22 TS% by position using the data at BReference.com:
NBA 56.6%
1 54.4%
2 55.1%
3 56.0%
4 57.5%
5 61.5%
The median PG's TS% was 52.4%.
As such, Murray's 53.3 TS% is slightly below average for his position. With a 54.0 TS%, Marcus Smart is a reasonable yardstick to measure Murray by. A comparison of the two players' 2021-22 results is below
https://stathead.com/tiny/HG9mI3FG%, 2FG%, and FT% are virtually the same for these two players. Smart has the higher TS% because he shoots a much higher percentage of his shots from beyond the arc, while Murray has a much higher FG% (45% vs. 42%) because he shoots mainly in the 2-point territory. The scoring is in Murray's favor because of higher usage, but he's also the Spurs' number 1 option and should get most of the opponent's defensive attention. I would expect that Murray's scoring is more consistent (i.e., he has fewer droughts) than Smart's because 3-point shooting is more volatile than 2-point shooting and because Murray gets to the line more.
Where Murray blows Smart out of the water is in playmaking and rebounding. He has a 41% Assist% and a 12% Turnover% to Smart's 26% and 17%. Murray was 5th in the league on Assist% behind Young, Luka, Paul, and Jokic. IOW is elite and with a better TO rate than those four. Murray's TRB% is at 13% vs. Smart's 6% and second to Luka among PGs. I haven't seen enough to know whether he's that much better a rebounder than Smart, but he's also a top steals guy, which indicates he has a nose for the ball.
Lastly, the advanced +/- stats are in Murray's favor this year, with his dominance over Smart offensively more than offsetting Smart's advantage defensively. Last year, it was closer, and before that, Smart had better numbers which, however, could be reasonably attributed to having a couple of years more experience on Murray.
As to the original question, I'd do the deal for three late firsts in a minute if we're taking Murray into the TPE or giving the Spurs non-core players. I think the numbers indicate he's better than Smart and clearly a much better offensive PG, but I'd have trouble trading Smart and three firsts for him straight up, even if Murray gave me a lot less heartburn.