I mean, realistically, there is no real reason LoT should be better on the lowly PCE than it is on the MD. The PCE is a much slower machine and the CDROM2 doesn't add anywhere near as much power to the PCE as the MCD does to the MD...but you do kind of need color. 
There's much more regular tech talk on sega-16, where experts break down the abilities/performance of consoles down the base mechanics of what happens for each frame. The consensus is that the PC Engine is fastest at animating or updating, followed by the Genesis and then trailed by the SNES, which apparently has such slow cpu speeds because of other bottlenecks like slow memory. The Sega-CD does have a fast cpu speed, but how the new hardware and Genesis interact is convoluted, with different was to do different things and again, some crucial bottlenecks keeping it from being insanely powerful all-round.
Lords of Thunder was tailor-made for the PCE hardware. You can't just replace every section of animated tiles with a scrolling tile layer, it doesn't all fit together that way. Many Sega fans try to criticize Lords of Thunder as being a poor port, but even though it lost a tiny bit of artwork, the developer actually did make use of the additional tile layer(s) and added new parallax. It turned out infinitely better than Final Fight did for color, yet that port is celebrated.
I've heard it proposed that maybe too much collision can be hard for the Genesis and is the reason for noticeable slowdown in games like Thunder Force IV (
which Genesis fans don't tend to be as critical of). Something like Air Zonk only calculates bullets and enemies and the background doesn't come into play. Star Parodia juggles screens full of animated bubbles, comprised of multiple sprites, which ricochet off of each other and the walls of the background, while still interacting with the player sprite and bullets. If you let the bubbles build up, you'll eventually see slowdown. The bubble section in LoT seems to do pretty much the same thing and the Sega-CD version spits out more crystals, creating a hell of a lot of collision to calculate (
). So it's not surprising that the game slows down there. The Sega-CD cpu is only 1.5 times the speed of the Genesis cpu, which already slows down in TFIV in areas with background collision, especially when a lot of bullets are onscreen (
).
Maybe my guess is completely off, but that is where the slowdown occurs. I'm no expert, but I do know that the most basic tech specs don't tell the whole story and games built from the ground up for Sega-CD like Keio and Bari-Arm also feature slowdown, and in situations that don't appear to be doing as much as Lords of Thunder. The Sega-CD's biggest strength is doing amazing 3D graphics, the kind that the PCE could never do. Is it so hard to believe that the PCE is capable of running 2D games that are difficult for competing consoles to handle as-is?
The Mega-drive itself is quite powerful machine. It's based off arcade hardware. With tricks it could make a lot more colors than 64 on display. That said it cannot display colors like the PCE. The Mega Drive has a LOT of power in terms of animation. It does things very smooth and with control to match. The Mega CD has the same processor just clocked faster and obviously the "Mode 7" effect but the standard MD could and can still do a lot.
The Mega Drive isn't based off of arcade hardware any more than the Master System. Especially if you consider the Neo Geo to be strictly console hardware. They just use cpus that were extremely popular/common at the time.
The MD is very powerful for the time, but the PC Engine is even better in terms of animation.
I don't get the fighting street reference however I know it's a launch cd title here in the states and not particularly good game.
Fighting Street is an un-moderated section of the forum for saying things that might be frowned upon elsewhere.
There are certain things the PCE does well and certain things the MD does well. Shooters the PCE just wins from what I can see. Even with parallax the system gets it done to an extent. Games like Vectorman or Earthworm Jim or Aladdin I don't see happening as well on the PCE. Every system has it's strength and weaknesses and I love that, not like today they are all the same.
The PCE wouldn't do the multi-directional parallax the same way, as that is its biggest weakness. The animation in EWJ and Aladdin plays to its strengths though.
I think this is more of a matter of those sorts of games, the high end AAA American developed platformers, coming about after nearly all development of platformers on PCE came to an end. Most PCE platformers are pretty low end, designed to compete with the Famicom-era.
Comparing the animation in Dracula X to Earthworm jim is pretty ridiculous. Richtor is small and walks like he has a broom handle shoved up his ass. I do see your point, there is plenty of power in the SCD system to make an Aladdin or EJ, but Drac X isn't a good comparison. The hold back wasn't technical, it just that the people making those sorts of games were either in the US or they were working on Super Famicom so the PCE got left out of the great graphical leap forward with EJ, Aladdin, that kind of thing.
I guess that you somehow missed the massive PCE, SNES and Genesis, screen comparison thread. Dracula X has characters with comparable levels of animation to characters in EWJ and Aladdin and
way more animation overall than either EWJ or Aladdin. Those games were original and chose to heavily animate the main character. Dracula X is designed around the Castlevania franchise. Richter walks like a Castlevania hero. The crazy detailed sprites with tons of animation in Dracula X is what compares more directly to the sprites with tons of animation in EWJ and Aladdin. Sapphire however, likely has
individual bosses with as many pixels of and/or frames of animation as either of those two games do
entirely.
A single attack animation from a single boss in Sapphire-
