I would sleep train nap 1 - meaning teach him he is to sleep in teh cot for a full nap. The only way to do this is to stop holding him for the additional hour. yes W2S is one method that teaches LO to stay asleep for longer (in their cot, not in arms) and what you describe here:
I put a hand on his back before he wakes at the hour mark and gently hold him down. I would have to be in there 10mins before to catch the wake up and wait at least 15-20mins holding him down to make sure he stays and transitions
is exactly the way the W2S method works (there are two methods this is the one I always advise). yes it takes time but it does teach Lo to stay asleep in their cot. I would give it a proper go, 3 days on 1 day off see what happens, if he wakes resettle then do another cycle 3 days on 1 day off see what happens, repeat.
If you feel W2S doesn't work you resettle at the 1hr WU. This means sooth him with your usual method (shush/pat or a rub, or stroke, a firm hand, key phrase etc) and you keep going until he sleeps or until nap time is over (or for 45 mins). If you need to pick up you do so to calm him down but you don't let him sleep in arms you make sure you get him down.
Sleep training takes time and effort, it isn't going to magically happen and he isn't likely to decide to suddenly do it himself. He will likely get OT during the training phase but that's okay.
I would continue to hold in arms for nap 2 but not let that nap be more than 30 mins because he mustn't be allowed to make up his lost sleep from nap 1 if he won't resettle by getting a longer nap 2 (if you want nap 2 longer then I'd suggest it not be in arms as you end up stuck again).
I would not move to one nap yet as it doesn't sound like he can handle the A time length needed.
This will cause a lot of OT, NWs and resistance at BT but I can be patient if it's just for a few days as he adjusts.
Honestly it is unlikely to be only a few days. Mine was as ready as he could be for the move ot one nap (ie always refused nap 2 and did super long morning A time), he was also a fully independent sleeper with a solid 2hr first nap and I had a great struggle and a lot of hard work to get him through the 2-1. His 2hr nap turned into 20 min OT screaming WUs and I basically had to grit my teeth and force him to sleep no matter how long it took and how exhausting it was. It was certainly more than a few days.