All these issues sound pretty common to me....your home inspector did a great job of what you paid them to do and that is scare you out of buying the house, so you bail, get another one, bail on that one, and they get 3 inspections out of you, before you understand these are homes.
The inspection report is often more of a status report these days, not a repairs list or a retrade tool....but see what you can get.
My thought is probably every home in the neighborhood will have the same issues if they were all built by the same builder.
None of these sound particularly like a deal killer to me. Even if you have to fix some of it, do it and move on.
Not sure what part of Texas, but these days in many areas you should feel lucky just to get the contract. Minor inspection issues are just the price you pay if you want to be an investor and you want to fix these things or you're just buying a house to live in.
ArcFault while a good idea, was likely not code when the house was built and likely not code for existing homes. Plenty of people all over the US and all over the world don't have GFCI and Arc Fault. Certainly adds some safety, but likely not required code to bring this home up to new standards of construction today by even the strictest cities that do rental inspections....even the ArcFault rules have changed over time.
My guess is the neutrals are just need to be split up. Remember an electrician wired this, approved it and city inspector signed off on it. Pretty common find. It is so common I think it must be acceptable in the electric trade. Is it good idea to split them up, yes, but pretty normal to see this and have home inspectors call it out.
Water heaters...I've seen them last 6-7 years on the cheap ones, and some I've seen last 40 years. Typically I see a lot get replaced about the 8-10 year old mark. Budget for it or buy a home warranty or have the seller buy you a home warranty. I wouldn't bail on a house because the water heater has aged....Just one of those capex you have to budget for. HVAC, Water heaters, roofs....they all have a lifespan.
Did you test for mold? How do you know it is not mildew? If it is mold, is the toxic variety. I would look at this and fix the problem so it doesn't continue. Something probably leaking. Maybe you need a new faucet. If mold scares you, have it tested and remediated. This doesn't surprise me at all, pretty common. This is what should propel you to do quarterly inspections, so things like this don't get out of control by tenants who don't care and don't tell you. Please tell me you've never been in a house, hotel room, camp shower, or school shower that didn't have a little black stuff growing in the grout. Pretty sure I've even seen it in a hospital.
Loose toilets...buy a wrench...tighten the nuts.....if you're buying investment property you are now a handyman. I keep adjustable wrench in my car....the rest of the plumbing I would fix, seal things up, secure things, connect things. Maybe the seller or their trade will do this for you.
No roof vents? Are there ridge vents, whirly birds, electric fans, solar fans?....nothing?...that surprises me a bit. Either you leave it or get some installed...or get the roofer to come back out and install.
To me none of these are worth terminating over....otherwise you loose your option, inspection, and potentially appraisal money and your time. That's easy $1000-$2000 right there that could fix most of these items....and what is to say you don't find the exact same issues in the next house.
Sorry to be a bit harsh and challenging...but to me there is no perfect house, no house without issues. If you find one that is perfect, something will break sooner or later.
Some of this stuff is like cars.....do you fill up at 1/2 tank 1/4 tank or 1/8 tank or when the red light is on.....Safer to fill up at 1/2, but probably not that many people do that. Do you immediately quit driving when the check engine light comes on, or do you stop the car, call a tow truck and take it to the dealer, or do you drive a week or two or a month and then take it to Shade Tree Tony to just let him turn the light out? Do you change tires for safety 1/2 way thru the life or do you run them to they're bald. Everyone is different, but I would also say even if you buy a brand new home, there are always things that the builder and home inspector disagree on...some things are standard practice and some things are gold standard.
Just figure out what you and your tenants can live with or without and provide them a good safe environment to live.