You certainly make a good point, I agree that the passing game wasnt what it is these days, biggest difference IMO is volume, offenses were much more balanced back then which affects the total amounts of TDs and INTs also.I think era has to be considered. Brees had the 10th most TD's during that time frame and there were 11 QB's during that time who had 100+ TD's. Tannehill had the 15th most TD's and there were 16 QB's who threw 100+ td's.
Also Brees's QBR of 87.5 was 11th best and there were 4 QB's who had 90+ QBR during that timeframe while Tannehills 86.5 is only good for 25th and there were 15 QB's who held a 90+ QBR during that timeframe.
But looking at the ratios, they're exactly the same at 1.4TD and 0.9INT... As for the ratings, I'll give you that, but you also have to consider SD had one of the best rushing offense in the NFL during his career over there... Im not going to flat out tell you their OL was better than Tannehill's because frankly I dont know, but I strongly doubt they were bottom half of the league.
All in all, Im saying they were comparable players at that point in their careers and I wouldnt have a problem with someone giving the edge to Brees with arguable facts...
But I certainly wouldnt call it apple to oranges and call people homers over it...