my work using gcpt showed the 3 signals used by people here, alone and in combination are inferior to simple SPY>SMA325

These Nasdaq momentum screens may well be a special case, but in the normal case it isn't.
(Probably is a special case. I get roughly the same overall results with 52 weeks as with 65 weeks.)

Dusting out a timing investigation spreadsheet I did a few years ago, using the S&P 500, it is certainly not the case. See below.

Adding in the GTT rule to the SMA timing greatly improved things. Try getting gcpt to add that and see what it says.

(Duh, I already have everything needed to incorporate GTT into my timing spreadsheet. Why didn't I think about this sooner?)

^GSPC (SPX, S&P500 index) weekly, 2/5/1950 to 3/10/2024.
All data is weekly.
Dividends included.
Weekly SMA. Sell when price below SMA. Buy at or above SMA.
Note: Setting the sell to -2% below the SMA generally reduced the number of trades and improved the CAGR.
OUT period return is 1 yr T-Bill.
Sortino MAR: 0%
slippage: 0.10% (per trade)
MaxDD is computed on the previous 52 weeks.
GTT disallows a sell if the 2 FRED indexes are both up YOY. RRSFS & INDPRO.

B&H
11.4%     CAGR
10.6%     Slope
-51%      MaxDD
1.05      Sortino
15%       stdev
Trades->  1
In %  ->  100%

65 week SMA (65 weeks = 325 market days)
 Only SMA                     SMA w/GTT
9.0%      CAGR                10.6%     CAGR
8.8%      Slope               10.4%     Slope
-26%      MaxDD               -26%      MaxDD
2.37      Sortino             2.83      Sortino
11%       stdev               12%       stdev
Trades->  165                 Trades->  67
In %  ->  73%                 In %  ->  83%    

52 week SMA (12 months)
 Only SMA                     SMA w/GTT
9.7%      CAGR                11.5%     CAGR
9.4%      Slope               11.3%     Slope
-19%      MaxDD               -26%      MaxDD
3.00      Sortino             3.60      Sortino
11%       stdev               12%       stdev
Trades->  201                 Trades->  73
In %  ->  72%                 In %  ->  84%    

43 week SMA (10 months)
 Only SMA                     SMA w/GTT
9.2%      CAGR                11.5%     CAGR
9.0%      Slope               11.3%     Slope
-28%      MaxDD               -26%      MaxDD
2.38      Sortino             3.53      Sortino
11%       stdev               12%       stdev
Trades->  225                 Trades->  83
In %  ->  70%                 In %  ->  84%