Why would Sema be safer than Tirz? Both are FDA-approved. And Sema seems to have a worse side-effect profile.
GLP-1 is the key "food noise" reduction molecule. Not GIP. With Sema you're only adding more food noise blunting, without needlessly adding Tirz's GIP, which is mostly responsible for non appetite suppression effects.
The GIP/Glucagon balance was key to making Reta work, when other attempts at Glucagon receptor agonist drugs failed (they caused some dangerous effects in fact).
Tirz has the native GIP sequence and works exactly like endogenous GIP, Reta very intentionally includes a GIP analogue that is much stronger. It's 9x more potent than endogenous GIP. That stronger GIP effect is needed to prevent hyperglycemia caused by Glucagon glucose release.
With both types, weak and super strong GIP in your system it's now a crapshoot which type attaches to which GIP receptor. Weak Tirz "natural" 1x GIP sitting in a receptor would block 9x strength GIP from Reta.
The GLP-1 analog in Reta is 1.4x more potent than natural, while in Sema it's 2.6x. A much closer match, and no risk of weakening the Reta GLP-1 effect, since a 2.6x strength Sema GLP-1 blocking a 1.4x Reta GLP-1 from occupying the same receptor will only increase GLP-1's effects somewhat, not weaken them.
Degree of GLP appetite suppression is hypothesized to be determined by the overall proportion of total receptors occupied (a number determined by genetics. probobly explains the wide variation in response) By adding more GLP-1 you're doing exactly that. A very targeted increase of just the molecule needed to suppress appetite, without randomly messing with other incretin hormone effects on insulin, glucose, liver metabolism etc.
The safest thing to do of course is just increase the dose of the GLP drug you're on, up to the max clinically proven safe in trials.