In shorts, buff the reload rate and add a more powerful HE shell to PLZ83, then raise its BR from 6.3 to 6.7.
Currently, PLZ83 has the weakest large calibre HE shell with lowest TNT equivalents (only 5.89kg TNT). While NATO M109s has 9.14kg TNT equivalents, Russia 2s3M has 10.14 kg TNT equivalents.
So PLZ83 is the only 6.0-7.0 SPH which is struggle to over-pressure well armored heavies such as King Tiger or Jagdtiger, etc.
All other SPH ranging from 6.0-7.0 does not have this issue.
There is a bunch of reports(acknowledged) to suggest more powerful HE shell for PLZ83:
Suggest BEE7 HE shell and BEE7 HE-VT shell // Gaijin.net // Issues
BEE7, 6.674kg Modified Comp. B (9kg TNT equivalent)
PLZ83 Should Be Equipped With BB/HE HE With Higher Charge // Gaijin.net // Issues
DDY1/PL66-152, 7.56kg TNT
PLZ83 Should Be Equipped With DDB2 HE With Higher Charge // Gaijin.net // Issues
DDB2/PL66-152, 6.09kg TNT
In addition, PLZ83 could reach 12s reload rate (currently 13.3s in game when Aced)
PLZ83 Have Semi-autoloader Thus Have Faster Reload Speed // Gaijin.net // Issues
However, Gaijin still takes no action. Gaijin denied the reload buff for balance reason, while in reailty PLZ83 could reach 5 rounds/min.
Comparing to M109/M109A1 in game, PLZ83 has better gun optics, better amour to stop 12.7mm HMG, better gun elevation rate and gun depression. Slightly better acceleration mobility. But worse reverse speed and HE round.
Comparing to 2s3M, PLZ83 has a 12.7mm HMG, better gun elevation rate and gun depression. But worse mobility and far worse HE round.
So a buff to PLZ83 might give it some advantages to current 6.3 SPHs, then a BR raise is considerable.
The suggestion is, buff the reload rate (from 13.3s to 12s when Aced) and add a better HE shell, BEE7 or DDY1/PL66-152 (I prefer BEE7), then raise PLZ83 to 6.7. It could reinforce the China 6.7 line-up.
Later Gaijin could implement a Taiwan ROCA M109A2 and put it into 6.3 as a stop-gap SPH.
M109A2 has little difference to M109A1 so it is an easy copy-paste work.
