I would say demigod is quite well balanced right now.
But I agree you that Regulus doens't fits very well in the cast.
1. He can kill oponents without being in their reach which is not possible for any other demigod.
He can kill over the half map with snipe. Can instant kill with mines.
Most dmg that could be done without beeing in danger on his own is Rook with towers. But you can see those and kill them, both things are not possible against Regulus. And minions are rarely able to kill demigods on their own 
2. He needs no skill. No really! Just lay mines where you could hit creeps or demigods and snipe anything on low health and run whenever something harms you. Comeone snipe hits over half the map with just 1 click. Not even aiming like with Elunes arrow in Dota is necessary.
3. He's the most egoistic demigod available.
Regulus has no support skills(beside a minor slow from maim or a slow from mines whcih never aplies since it kills instant). He never tanks. He killsteals (with regulus this is the only situation where this term really fits) which gives xp to the most unimportant demigod on the team.
Even Unclean beast tanks, which does something for the team...
Summerisation: Its not fun to play against Regulus in any way. No problem with any other demigod since all could be killed if they can kill you.
My opinion on possible fixes:
Mines are a very strong aoe effect against creeps and kill often instant.
You can't do anything! against being killed by it beside stacking Health (which isn't even is a good counter).
Against a fireball spamming TB (and every other skill) there would be at least two more ways: running away (stacking running speed) or killing him (stacking dmg or attack speed gear)
Possible fixes:
- Let demigods only be hit by one mine simultan or
let the skill only lay one mine (with no aoe effect) or
reduce the damage drastical.
Snipe has a too long range from startup which makes it able too kill/finish even with only one skillpoint in it.
There is no real possibility to evade it: runing kills you even more. Teleporting doesn't stops snipe even if it would be out of range after your landing. With two or more Regulis on a team having half of your life means an instant kill from anywhere on the map. With the gps bug
even the retardest people will "simultan" snipe you since can't get out of vision of the second and following regulis.
Possible fixes:
- Give snipe a low starting range on skill level 1 which improves with more points (so lvl1 snipe would be quite pointless)
- Make it hit the first unit on the track
- Make snipe unable to hit target when they run in the shadow before the bolt hits them
- Take away the gps bug skill (forgot the name) so consequitive snipes are at least impossible
- Make it impossible to hit with more than one snipe for 30 secs (30 second snipe immunity)
- Invert the range/dmg ratio so snipe makes more dmg in close combat and deals only minor dmg when hit from across the map (would be a little more realistic
) or give it an increasing miss rate with higher ran of the target after x yards