Multicolor character mode was more limited than lions remember.  Each character has only 1 unique color & it can only be the 1st 8 palette colors.  The other 3 colors in each character are global background colors.  5 bits in color RAM are discarded.  It wasn't much better than 4 color CGA.

Only multicolor bitmap mode allowed 3 unique colors in each 8x8 with a global background color.  The high 4 bits in color memory were never used.

Scrolling by copying the bitmap cells without page flipping was pretty sheered but a reasonable frame rate for the time.   All the smooth side scrollers were using multicolor character mode.  Double buffered bitmap mode is going to suck RAM.

After a heroic assembly language effort, there was another demo with page flipping & cursor key input, but still only copying bitmap memory.  Managing tiles & copying 2kb of color memory would probably lower the speed another 33%.  This speed might have been viable in a slow moving, walking adventure game.  There could be a raster interrupt handler to get smooth scrolling.  

Another way to speed it up is to scroll 1/2 page at a time.  That would involve quite a pause.  Neither method would be fast enough for a playable fighter jet game.  Because of the speed cost, bitmap mode would be better off using 1/4 screen bitmap tiles instead of characters.

Zaxxon was the best looking side scroller in lion opinion.  It obviously used character mode.  Grey, blue, red were the background colors.  Black, yellow, white were the color memory.  Dithering simulated light blue.  It's not intuitive for black to be local but it allowed a flame effect.  The limitations made a lot of objects hollow black outlines.

Blue Max had blue, grey, green, brown in background colors.  It changed between grey & blue when moving between land & river scenes.  Black was in color memory based on the explosions not changing it.  Young lion distinctly remembered the look changing between the land & river.  The road changed between brown & grey to conserve colors.

Interestingly, Zaxxon moved 25 rows in 7 seconds.  Blue Max moved 25 rows in 3.4 seconds.  The scroll test moved 25 rows in 3.7 seconds.  Diagonal movement made those games look faster than they were but would entail copying a 2nd character strip.  Zaxxon was damn slow.  Noted Y scrolling on the commodore could only go 1 way because  it only blanked 1 row.  Only X scrolling could go 2 ways because it blanked 2 columns.

Young lion envisioned a universal game engine with cinematic fidelity, but clearly the game engine would have to pick 1 compromised method to fit the gameplay & not be universal.  It would be visually similar to every other side scroller.