You clearly don't understand the process and the reason WHY T4 helps to the GH... The GH wil CHANGE the T4 into T3... and exactly THE PROCESS of thyroid activation (making t3 out of t4) is the thing which is helping GH (well very simply said)...
So.. There are three possibilities:
T4+GH: T4 will be activated, T3 will be produced.. result: Better use of GH, higher T3 levels which means fat burn (this is answer to your question..) and more consistent T3 and T4 levels which means homeostasis maintained (at least up to certain acceptable point when injecting hormones)
GH alone: GH would rise T3 levels which means negative feedback, T4 levels are lower that they should be to persist T4 to T3 ratio which means homeostasis broken.. GH potential not fully used, T4 to T3 conversion lowered because of lacking T4 amounts
T3+GH: negative feedback from T3, T4 levels very much lowered, T4 to T3 conversion stopped or very low... waste of money...
So guess what option is the best one? I would say if you wanna use GH for fatloss, use it with T4 or save your money and buy clenbuterol or ECA combo... or just clean your diet and add more cardio LOL
And this is very easy to explain as well.. and has nothing to do with hypo
Body (without GH present) would convert (activate) only specific amount of t4 needed at the time. So you can eat pound of t4 a day, your t3 levels wont rise beyond certain level... And t3 is the active thyroid hormone which is responsible for fatloss...
Only difference when GH is present is that much more T4 will be converted (well it is the thing GH does) so the T3 levels will be much higher, so fatloss will be much better..
Now lets take a look to T3 + T4 combo... Of course this statement I an writing is dose dependent... Because if you take t3+t4 without GH I would say you are wasting T4... because again.. body will produce T3 out of T4 only until it detects that levels are high enough... So if you are supplementing T3 itself... levels are high enough all the time, so conversion is NOT NEEDED!
And again... taking GH+T3+T4... as described above... if levels of T3 are high enough none of T4 would be activated... Only difference is that with GH present, the "high enough" means a lot higher than without GH present... So there is a possibility that SOME of T4 will be activated even if active T3 is supplemented. BUT! WHY would I want to do this? I can take just T4 alone, GH would take care about activation and T3 levels will rise WITHOUT supplementing T3 to the SAME LEVEL! Only difference will be that MUCH MORE CONVERSION will take place and guess what...? GH BENEFITS FROM IT! So... I have high T3 levels and better GH usability with GH and T4 ONLY!
Of course if someone is taking more T3 than levels required even with GH... he will get better results in terms of fat burn that GH+T4... but it might be getting a little rough for the thyroid gland and I don't see any reason why somebody would want to ruin it...