Imho pixels fucking suck. Repairability is really bad, so as soon as anything has issues you need a need phone. I would say the answer to your question heavily depends on your daily battery life requirements. If you wanna stretch the phones overall life, set a 70-80% charging limit to damage the cells less. (If that is even possible with the new models idk, you didnt specify yours...) If you treat it well and turn off all the battery sucking toggles to extend the time before needing to charge, then 4-5 years might be doable.

I tried Graphene for a bit but ultimately couldnt put up with pixel devices anymore and went to calyxos on a fairphone. Not having a swappable battery or extendable storage is just not fun. If you want a 10 year phone get a fairphone. The 6 just came out and is very well priced in the EU.