Nah, the Medieval ~> Renaissance gap isn't a full transition. LongS to muskets is only a change from 21 combat to 24. Pikes get bumped up to 25 through the lancer. It seems to be a buffer zone to bring everything on an equal level before heading into Industrial. If you didn't get any iron earlier, this is the chance to get some infantry on the board. Pikes get an upgrade, too, but an obvious push out of the role of fill-in infantry into a more specialized role.
Crossbows/knights are OK, too. The archer line is strong already and the gap isn't noticeable (although pre-G&K the archer to Xbow was way too long, so Cbows were a welcomed change). I think another mounted unit after the knight would be overkill as well. If anything, it would be a further [indirect] hit against the lancer making their specialized role non-existent.
The lancer ~> anti-gun is a bit long. It is odd, too, because spears come before horsemen and pikes before knights, yet anti-tank comes on the same tech as WW2 tanks, and nothing for WW1 tanks. And as I've seen mentioned before, once you get anti-tank guns it is only 2 more techs until helicopters. Really no reason not to move it earlier in the tech tree and probably an oversight from vanilla when all the WW1 units weren't in the game.
Frigate ~> battleship seems too long as well. The gap is most noticeable when one player gets battleships before another. Frigates can have tons of promotions thrown on them and battleships will still plow right through them forcing you to avoid naval battle until you get battleships as well.