Hey Lopes
I suspect that Oskar of Retra will chip-in on your comment about Retra support and ageing. I was slightly surprised by the comment which doesn't really match what I have seen on WP.
If you have a look on the Retra strobe thread you'll see that they are very pro-active at offering help and assistance. They have not been operating for very long so it's hard to say what the medium/long-term might be. But, so far I - and others - have found them unfailing helpful. Oskar and the Retra team answer emails quickly; they chip-in on WP often - and they support their strobes rather ingeniously by being able to Bluetooth them for firmware updates and for diagnostics. The manual and support materials are very good. (Inons by contrast are horrible!) And they are almost bomb-proof in build and design. The one year initial guarantee is extended to 2 years by keeping the firmware upto date.
A nice touch too, I thought, was a while back Retra extended all/most warranties to 2 years because of COVID and buyers not being able to dive. I can't recall the full detail now but it covered my strobes bought in Feb 2020.
I can't speak for Sea & Sea. Sorry, no personal experience but you'll find lots of thoughts on various threads if you search for Sea&Sea strobes. Not all positive....
On the Inon, I have no idea what their direct support might be like from Japan and I've never had to contact a local dealer for support. I never had a problem with an Inon strobe over something like 15-20 years (Z220, Z240 models) so never needed serious support. Speaks volumes. There is a very broad user base and, again, if you do a WP search on Z240 or Z330 you'll see there is lots of advice and info from WP members - and parts, generally are not too hard to find.
Just one other thought: I can light reef sharks when they come within, say, 6' - which they do here. (got to say, nicely with the Retras) But I really have doubts about being able to light a whale shark or whales with any strobe. That's ambient light stuff. Strobes just don't have the power to light really big things. Maybe worth bearing that in mind (and forgive me if I'm offering egg-sucking lessons).