AIs are awesome (I have one) and so are TRGs (I had one). They are well built, tough as nails (the AI more so than the TRG), and as accurate as any custom.
However, if you are doing PRS comps I think the needs requirement is a bit different. Yes there are a few guys out there who run AIs quite successfully but word on the street is they are not stock guns (lighter triggers, etc.). Seeing as you are looking to replace a 300WM you probably are not doing PRS matches with them.
If you don't shoot in really dusty conditions all of the time a Defiance/ARC/Bighorn is going to do all that you need to do for less money.
You can't go run with an AI though and if you get the AXMC and don't like it you can probably recover the majority of what you spent.
I am a member of team AI and have shot an AX for 3 years and shot out a dozen or so barrels. I shoot a standard trigger on a standard rifle with standard barrels. The only modifications I have done to date are tune the trigger using the adjustment screws, remove the plastic forward grip, and add a HRD gear ARCA Swiss/RRS rail and SAP +2 round holder. I've never finished outside of the top 15 for a PRS season. Last year, I won K&M with a stock 6.5x47 and won Allegheny Sniper Challenge with a stock 308 shooting 118LR. As a rifle system, it is as accurate as any custom out there. As to the durability, I would disagree. The finale last season was very tough environmentally. Not 1 AI that I know of had an issue. Many customs went down (mainly trigger failures). I will admit that there are definitely some improvements that could be made to the AX as far as a rifle for PRS but in reality, that is not what the rifle was designed for. They are designed to meet a military spec and just flat out work no matter what. I own a lot of customs and 3 AIs. The AIs are the only ones that have never gone down for me in any way, shape or form. Usually the weak point I've found in my customs are the triggers and bolt assemblies (bolt fitment, handles, firing pins, ...etc). What I like about the AI is that barrels are abundant and easy to replace and the system will return to zero when changing barrels out. If you need a new barrel, you can have one in 2 days, not 2 months or more depending on the smith. They run with AW mags all the time and never skip a beat. Finally, everything about the system is adjustable. The downfalls are that it is a stock rifle... You can't pick a trigger, chassis/stock, ...etc. Also, they are expensive.
If the chassis is for you and you can swing an AI, I highly recommend the AXMC for the OP. It can (would say will but everyone knows you always"need" another rifle) be the last rifle you ever need because you can swap barrels, bolts, mags and run anything from a BR to a Lapua mag. If the 2 stage trigger, price, and/or other limitations are a no go for you, you can definitely build a custom that can equal it in accuracy and possibly in reliability.
OP, if I can help out in any way, let me know. I will give you a straight answer on either side AI or Custom and if I have no experience with something, I'll tell you. If you are close or going to a match I'm shooting, you are welcome to shoot any of my rifles. Just shoot me a PM.