Alright, after continued playtesting despite what josh56 would be saying, all evidence points to the contrary.
Okay so it would be good to know a bit more about the context you've been playtesting these in. It sounds to me like you're playing 4 player games? This would explain why you're not seeing games where Bulgrim is super op. I don't have much experience with 4 player games so someone else can probably add more but as far as I'm aware the winning strategy is often to just get Silvers and a few actions and green asap because the games end really quickly, so that could explain your findings.
At a cost of 8, Bulgrim was only bought twice, even when i had enough to purchase, because our games have a very short duration & there is hardly enough time to reach a buying power of 8 & already/ instead be buying provinces.
The only two options were to slow down play (nope), or use silver spamming with masterpiece, which has better avenues of victory anyway.
Of the two times that Bulgrim was used, he mainly used his "half golem" ability, which had little effect against a silver/ masterpiece build. And only accounted for 3-4 VP at the endgame using a market/peddler build.
My opponent really is fixated on a silver build, & even the avatar i made to benefit a silver deck was used only twice. Not to mention he was the only player able to regularly afford the avatar.
If you're playing 2 or even 3 player then perhaps you had some particularly weak kingdoms with not much going on or maybe just missed the optimal strategy, unsupported Market/Peddler isn't the best but obviously I haven't seen the games so I can't really comment on that. Maybe post some kingdoms you played and explain what everyone did so we have more to go off? An unsupported Masterpiece deck shouldn't win a 2 or 3 player game in my experience, but Masterpiece might be an amazing card in 4 player I don't know. I'm also not sure what you mean by slow down play.
Also you mention a Silver/Masterpiece build a few times, did every game you played feature Masterpiece? If your playgroup finds Masterpiece to be a dominant card then maybe you should shy away from including it when playtesting because it might be skewing your games.
So a little more on Bulgrim, note that what I'm saying is looking at the context of 2 player games. In terms of it's power level 3-4vp that doesn't add a dead card to your deck is very competitive with Province and would have to cost $7-$8 on it's own, it's also not uncommon that you end up with 20+ Actions in your deck either in which case Bulgrim will be worth even more.
Calling Bulgrim's effect a "half Golem" is a bit misleading as getting a free half golem (i.e. one which doesn't cost a card space in hand or an action to play) is on very similar power level to having a self-scheming Golem, arguably better as there is no risk of turning over 2 terminals and prematurely ending your action chain. Golem costs $4P so self-scheming Golem would have to cost $5P or even $6P, which is obviously not directly comparable to $8 cost but is very close. You seem to be saying here "I paid $8 and only got a half golem and 3-4vp" I'd be saying "I got a half golem and 3-4vp and I only paid $8" Hopefully this helps to explain why people are telling you that it's too good.
In terms of design I would say that you pick the golem option over 90% of the time, very occasionally taking the money and almost never trashing. The +1 card and +1 Action options seem useless next to the golem effect. I would strongly consider whether the other options are worth all the extra words with them being so situational or just scrapping the golem effect for something of more reasonable power level.
I do agree that it's more important that these are balanced amongst themselves than balanced compared to regular kingdom cards (although I see no reason why these shouldn't be both) but I don't think that is possible in their current form, one will have a vp effect that is better than the others on a given board and will give the player with first choice a huge advantage. The first step to making these balanceable is to either scrap the vp aspect of them as Landmarks cover this space really well already, or if you insist on keeping it change it to a threshold to mitigate the effects of one getting out of hand and being unbeatable, something like "Worth 5vp if you have 10 Silvers in your deck at the end of the game".
