That's a frustrating situation, but unfortunately pretty common with techs who don't specialize in vintage-style setups. You're absolutely right about several of your observations!


Your Analysis is Spot-On:


3-Saddle Bridge Issues:
You're correct that 3-saddle bridges require compromise. The "sweet spot" approach is exactly right - you're balancing intonation between two strings per saddle. This is why many players eventually upgrade to 6-saddle bridges.


String Gauge Impact:
.012s are definitely heavy for a Telecaster, and yes, they do require higher action to avoid buzz. The increased tension and vibration amplitude means you need more clearance.


Fret/Setup Relationship:
If you have fret buzz with proper neck relief but not on open strings, it's likely:
1. Uneven frets (some high, some low)
2. Action too low for your playing style
3. Neck relief not optimized for .012s


What I'd Suggest:


Immediate Solutions:
1. Check neck relief first - with .012s you might need slightly more relief (0.010-0.014" at 8th fret)
2. Raise action gradually - start with 2.2mm low E, 1.8mm high E at 12th fret
3. **Compromise on intonation - slight sharp/flat is better than constant buzz


Long-term Options:
1. 6-saddle bridge upgrade - solves the intonation compromise
2. Professional fret level - if frets are truly uneven
3. Drop to .011s - still heavy but more manageable


The Tech Issue:
A good tech should have explained these trade-offs upfront. The fact that he said the neck was fine initially but blamed it later is concerning.


I actually went through a similar situation with my Tele and documented the entire troubleshooting process with specific measurements and solutions: The Ultimate Guide to Setting Up Your Telecaster | Blog


The guide covers exactly these issues - 3-saddle bridge compromises, heavy string considerations, and the relationship between action, relief, and intonation.


My Question for You:
What's your neck relief measurement currently? And are you getting buzz across all frets or just certain areas? That would help narrow down if it's truly a fret issue or just setup optimization.


Hope this helps - Telecaster setup can be tricky but very rewarding once you get it dialed in!