All, First off, let me say thanks for any information that you may be bale to provide. I am looking at purchasing my first “real” bike and know absolutely nothing about bikes or what I should look for during the purchase, so please forgive my terminology. I am 6’3/190 and am planning on using this for fitness and general enjoyment riding in SE Ohio. I do not plan to race, compete or otherwise. I’m 50 years old and due to lingering aches and pains from the military, running is not much of an option any longer. The vast majority of my riding will be alone or with a few friends on bike paths, commuting on city streets and the occasional packed dirt/light gravel trails. I do not plan to take this onto single track or general MTB terrain, nor do I plan to go bike packing or for extremely long rides. I do tend to research about purchases prior to making them and I have researched quite a lot on this subject and this forum has provided me with a lot of information. I recently got fitted (measured), and based on the measurements the two bikes that most closely fit me were the Salsa Warbird and the Cannondale Topstone, both in XL. I have tried the Topstone, which I enjoyed although it was only available in Large. I am not able to try a Warbird as there are none available in my area to test. I have also tested the specialized E5 Comp and the Trek Checkpoint ALR5, which I did not like. One other bike that has been on my radar is the Canyon Grail AL 7.0, which of course I have not been able to try Another option is to go with the Warroad and the Synapse. The main concern for me is comfort as one of my issues is lower back problems. So a more relaxed position is key. This bike is going to have to last me for a long time and I want to ensure that I get something that is geared towards my style of riding and that it will be money well spent without the need to upgrade something in a short timeframe. Additionally, if at all possible I would like to keep my limit at $2500 or below as much as possible. I know each of these bikes mentioned fit well under that number but again, I’m not fully understanding the need for a 105 vs Apex1 vs Tiara etc etc or if I would even need a hydro system for my applications. Although I think I would prefer to keep it a 2X instead of a 1X. Again, thanks for the assistance and look forward to learning from everyone.
Fit: If you want to get an idea of how different bikes will fit, you'll have to look at the manufacturer's geometry charts. Start with the bikes you know have the fit you want. IMO, the most important numbers for fit are Stack and Reach and the seat tube angle. There are guides that explain all the measurements, like this: https://www.bikeexchange.com/blog/bike-geometry-charts-explained-guide
When I was looking I ended up making a spreadsheet to compare the numbers for different bikes. I wanted a fairly upright position and a lot of bikes had stack heights that were much lower than I wanted, which helped narrow the field. I lucked into a deal on a Niner RLT which was one of the candidates on my short list.
Components: I have no SRAM experience so can't speak to the great Shimano/SRAM debate. The biggest difference between the current Tiagra and 105 groups is the jump fro 10 to 11 speeds. Either would probably be fine for the riding you want to do. As you ascend the levels you get a bit more precision and a bit less weight, but it's not a night-and-day difference.
I don't have experience with mechanical disc brakes. I've been happy with the hydraulics on my mountain bike and gravel bike. It doesn't sound like you plan on huge descents so either would probably work for you. Try riding an example of each, even if it's not on a bike you want.
Endurance road bikes: The big limitation there is maximum tire size. For mixed-surface riding I’d suggest being able to accept at least a 40mm tire. You can always go narrower if you end up riding mostly roads.
Wider tires are more comfortable. I'd recommend a bike that can take 38mm tires, minimum. These will handle the surfaces you mentioned while still allowing decent asphalt speeds. I own a Blue Prosecco and it seems like a frame you'd like, tall headtube, shorter reach, can fit up to 38mm tires and is comfortable on both jeep trail and asphalt. I can easily keep up with the 18~20mph group on road rides. For me, the position is a little too upright. I prefer a lower front end and a touch longer reach for a better aero position. I also want fatter tires because of the sandy patches often found on Florida gravel roads. Giant's Revolt line are nice bikes, they start at $1000 (aluminum) and go up from there. The carbon line starts around $1800. The Cannondale Topstones are nice. The GT Grade is something to consider, they have both carbon and aluminum models.
Having owned one, I’d stay away from the Synapse. I had a carbon Rival model... heavy, harsh riding, limited tire size. The Topstone is too much of a road race bike geo for what you want.
Being 6’1”, 240 and Having plenty of lower back issues myself, I would strongly suggest a bike that can handle 45mm tubeless tires and a more relaxed riding position so the Warbird is the only one you’ve listed that would get that done.
I don't know a lot about the Salsa bikes. I thought I knew this though. The Warbird is considered a race ready geometry bike where the Cutthroat isn't. Why aren't you considering the Cutthroat. For sure you want 2x I don't think you need hydro brakes though but I really like them. Zman