According to Dragon Ball Heroes Ultimate Mission X, Xeno Goku is able to transform into super saiyan 4 and at some point he was able to transform into super saiyan god. So he has to know which transformation is stronger, and in the Dragon Ball Heroes continuity super saiyan 4 and super saiyan god can indeed be compared since both exists there. Then, which tranformation is stronger? Xeno Goku super saiyan 4 or Xeno Goku super saiyan god transformation?
We don't know for a fact as to whether Xeno Goku was referring to himself using the Super Saiyan God transformation or him referring to a Goku of an alternate timeline using the same hence, there are no feats to make an accurate comparison between the two.
Hence, it would simply end up in a SSJ4 vs SSJG debate which is impossible to determine with a definite certainty as to which of the two transformations is stronger as there aren't any official multipliers to conclude with a definite answer. However, based on the following facts and events that happened in the Dragon Ball Z and Super(Which are considered canon), I believe the SSJG transformation might be stronger.
- Super Buu was about the same level of strength as SSJ3 Gotenks who was substantially stronger than Goku (SSJ3 Goku struggled against Kid Buu).
- Ultimate Gohan was a lot Superior to SSJ3 Goku and Buuhan, the combination of Super Buu + Ultimate Gohan is on a whole another level.
- I believe scaling SSJ4 Goku to be as strong as Buuhan is too much of a stretch but even if that were the case, SSJ Vegito easily manhandles Buuhan without any effort.
- Post Buu Saga trained Goku after getting defeated by Beerus stated that even a fusion between Goku and Vegeta wouldn't stand a chance against Beerus.
- When the SSJG ritual fails the first time, Gohan stated that Goku's level of power was so intense and something he had never sensed before. Note: This was even after seeing Vegeta fight Beerus(Who surpassed SSJ3 Goku) and also taking into consideration his power as Ultimate Gohan and even all the Buu saga characters.
- One can easily conclude the Battle of Gods arc Vegito would be substantially stronger in comparison to the Buu saga Vegito who easily manhandles Buuhan and once Goku turned SSJG, he thought he had a chance against Beerus making it even stronger.
One would ask why Xeno Goku doesn't utilize that form over the SSJ4 form. However, it has been established that one would require special training(Goku and Vegeta with Whis, Toppo with Marcarita), to master the usage of this divine ki. So perhaps Xeno Goku cannot tap into this form anymore.
As stated earlier, my answer is based on factual evidence from Dragon Ball Z and Dragon Ball Super which are considered canon. Since there are no actual multipliers for these transformations, one cannot conclude with a certainty as to which form is stronger.
This is the short answer: In dragon ball heroes xeno goku did end up doing the god ki ritual seen in dragon ball z battle of gods (movie) and dragon ball super (anime) and so that’s the furthest he got into the whole thing so he has god ki but can’t go ssgss cause of choice for some reason I don’t know why but I do know for a fact that his ssj4 has god ki so it is just as power full or a bit less than ssgss but whay more powerful than the ssj4 used in gt