Lets see... Coral is coming off his worst year, but that's probably because Orlando's boys were depressed last season... He did have two really nice years so far, though. I would imagine his long term trend will put him below 1.25 WHIP, ERA+ over 135, and FIP in the low 3s. A very solid #2 type pitcher but probably not a perennial all star. Orlando has him locked down until 2057 at $4.3M per year, which is good in general but not great for an arb deal. An arb contract that high tells me Coral is probably going to be a pretty expensive player to keep when it comes time to extend. Still, getting a pitcher like this, especially when he's been one of the best pitching prospects in the post 2048 draft world, is worth a lot.
Zachary Mills had a good season last year, but I imagine that will be toward the top end of what he's capable of... Though I assume he'll get plenty of opportunities! Carlos Vázquez projects as a solid starter at 2B and I'd guess he moves into that 2-2.5 WAR range on average. Blockhead looks like a decent pitcher relief pitcher (or maybe an SP in your system?). It is hard to place value on guys like this because RP of his potential are available on a yearly basis in FA and don't cost all that much. He'll have decent value for his 490k years and if you can get him under contract for under a million that'll be nice. The downside is he hasn't really pitched well in the minors yet. Probably hard to tell. The real big piece of the puzzle is Karshev, but it is still too early to call this one a win either. If he turns into an the all star catcher that his potential shows, then you can view this trade as a nice success. If he busts
So in summary:
Hel got a good young #2 pitcher. This would be a better deal had Orlando been able to lock him down for $2M or less during his arb years, but he's still pitched 2 good years and one decent year so far.
SF got a decent RP prospect, a #4 or #5 SP, a solid starting 2B and an elite C prospect.
I think it was a win win trade in that Orlando already had a good system in general and could afford to move a number of guys who probably would have never seen WBL time for him, in order to secure one of the best prospects at a premium position. Vasquez, Mills, and Blockhead probably wouldn't have seen much WBL time for HEL (maybe Vasquez) so he didn't lose much there. Swapping CORAL for KARSHEV is pretty even in that they were both great prospects at premium positions. SF was able to play the numbers game and secure multiple starters (which they needed) and also secure a premium prospect on a better timeline for them (would Coral have mattered to you in 2051 and 2052?). I'd say SF got more value, but that's also because they were starting with more needs. If Karshev is an ALL STAR then the value tips towards SF. If he busts, it tips toward HEL.
I bet both parties are happy with the trade.