I agree with Jeroen.
Why would you as a DBA want to give in to what the DEVELOPER may suggest without any evidence ? It is not a turf war but you need to find out where the bottleneck really is.
It may be that the DEVELOPER is on right track. So ask him/her why he/she is suggesting that !
You need be convinced too and with some facts to back it up. So you can get the baseline before and verify the results after you tweak any configuration.
Running sysmon periodically is good start.
If you have third party tools like Surveillance by BradMark, DPA by SolarWinds, proactive DBA from WhiteSands, etc use them. You may also tap ASEMON that is freely available.
HTH
Avinash