Many manufacturers and some agencies require AN/DP prior to moving to CCR
You have 100% O2 and resultant hyperoxia risk
You have hypoxia risks
You have a mixing station on your back that takes bandwidth to monitor
You don't need any of that to bimble around in 30ft of water sharing gas, learning good kicks, shooting SMBs, and learning how to be a better buddy. That blinky HUD and handset reading 1.01, 1.35, and 1.32 (bad news) are nothing but distractions from the purpose and goals of fundamentals.
Even if you did want to combine these classes who has the time? GUE-F is commonly a 4 day class, sometimes stretches to 5 if split into 2 weekends with one of those weekends being 3 days and the other 2 days. CCR Mod1 air diluent is minimum 5 days, sometimes 6. So combined you are looking at 10 days minimum. At $300 day for a 3 person class that's $3,000 with no CCR yet. Realistically this kind of zero to hero Fundies plus CCR is probably 2 solid weeks split in two by 6 months and 25-50 loop hours of practice time. And there's no trimix at all in this $3k effort yet.
By mainstream OC tech you mean on trimix? As long as there are CCRs there will be OC bailout and when you actually bail at 200ft (or in a cave) you'll appreciate having a solid OC foundation. There are people who don't have that and go from AN/DP on air to Mod1 (air dil) then Mod2 (finally now on normoxic dil) on CCR. They are sometimes a task loaded CF when they bail on their CCR.