There were some great arcade conversions on the Amiga, but most were not:
1). Atari ST version invariably leaded, and seeing as most development teams had maybe six or so versions to do, they didn't have the time or inclination to make the Amiga version as good as it should be. Most development teams were simply paid a one off fee to get the conversion done. If the teams were not going to get any extra money to make the Amiga version better, can you blame them for not bothering?
2). Invariably the wrong teams were assigned to do conversion work. Its down to money. If Binary Design (Richard Aplin) doesn't give a better price than Tiertex, then Tiertex will get the job. And just look how shit they were!
The Amiga suffered mainly because of the influence of the Atari ST, end of! They coded for the lowest machine (and most popular at the time) then ported to Amiga.
The Megadrive was a good machine, and Strider on the Megadrive was infinitely superior to that of the Amiga version, same with Ghouls n Ghosts (although the Amiga music was far superior to the Megadrive and Arcade). This wasn't because the Megadrive was better, it was because Sega and Capcom had a little more pride in what they produced. US Gold didn't. They spent a shitload on a licence then needed to recoup that money as quickly as possible.
Its a simple equation really. Compare some individual development teams that wrote software for the likes of Psygnosis (not the last of their games obviously!). Maybe the gameplay was suspect on some of their titles, but you can't deny the technical prowess behind them. Terramarques Elfmania showed what the Amiga was capable of, it certainly made Streetfighter 2 look crap!
The Amiga was fucked by the Atari ST. The Amiga was fucked by every clown that went and bought a shite Tiertex, Kremlin, et al conversion. If people had voted with their money, people like US Gold and Ocean (The platform game kings!) would have had to sort their act out. Ocean did at least try before they got swallowed up by Infogrammes, with genuinely good attempts such as Robocop 3, Inferno, TFX (not amiga but PC), Hook. US Gold, got swallowed up by Eidos too easily because they had been rumbled, people were hacked off with their lame conversions.
So next time you decide to slag off an Amiga arcade conversion and think the machine simply was capable of it, I guarrantee theres at least a couple of independent games out there that prove that theory wrong.
Tiertex and early Teque.... did more damage than you can possibly imagine!