I think there are generally two schools of thought when it comes to BBEGs: those who view them as a solo boss and those who don't. I fall into the latter category, as exemplified in hawkeyefan's post. I wouldn't argue that a 10th level party cannot chew through 135 hp with ease, because they can. A lich has access up to 9th level spells that the DM is free to switch to suit his own strategies and needs; that leaves room for a ton of different tactics for the lich to use on the party to ensure they are kept pretty busy (and spending precious resources) before they even reach it - that's just how I'd run one. I'd never have it sitting there waiting to go toe-to-toe with the party, there are other brutes that serve that purpose for a lich (golems, summoned demons, etc.)First, none of that affects the lich's CR. A CR 1 guy (albeit with with the right magic item to cast wall of force) can do that. That doesn't mean the surprising intelligent and rich commoner is an appropriate challenge for the party or mean its effective challenge is twice as high as it should be.
And it doesn't mean that when the party does finally get to him, he's going down in one or two turns.
There are a few assumptions being made here. I realize the wall of force is but one defensive tactic in a lich's repertoire, but it is a good tactic to divide and conquer. If we're still using a 10th level party as the example, they won't have teleport, but they will have dimension door, misty step, etc. So first they need to discover the wall of force is even there, then bypass it with the various methods mentioned. Misty step allows only the caster to travel, and dimension door allows the caster plus one if the caster's carry capacity is sufficient to bring another. So again, the lich has succeeded in dividing the party and had them use actions to discover the wall of force. To take this a step further, going with a prepared lich with a game plan, the lich has already cast mislead on itself so those who bypass the wall are faced with an illusory lich. Not to mention other safeguards like glyph of warding, programmed illusions, guards and wards, etc. And I haven't even used any 7th, 8th, or 9th level spells yet, not to mention other summoned minions (all within the lich's means straight out of the MM).Second, going through your situation, the lich casts the wall of force then the next round teleports away.
This assumes that the lich beats the party with initiative and can block all of them with the wall. And it presumes the party can't teleport, dimension door, Shadow Step, misty step or otherwise get passed the wall of force in the intervening round. Those are both pretty big "ifs".
At any rate, this is just a simple example that I might use. I'm not saying a 10th level party would lose to a lich, just that I doubt they would wipe one out in a single round or two. Nor am I trying to change your mind about it, this is all just spitballing.
I agree, there does need to be a balance between smart and fun villains - and this falls squarely on the DM's shoulders to make that happen, not some pseudo-mathematical CR guideline. There's something to be said for recurring villains, and smart villains should have escape plans. Not all BBEGs need to be a fight to the finish, at least not in the first encounter or two. YMMV.Third, really, if played smart he shouldn't even be in the tomb. Unless the party makes it through undetected, he should just bail, activate the self-destruct, and set-up shop elsewhere. Or treat it like a pest control problem: seal the tomb and bug bomb the entire dungeon: a party that can't breathe isn't a problem, and as an undead he's unaffected,
But, like dragons dropping boulders on the party from 650 feet in the sky, that is no fun for the players. There's a balance that has to be struck between smart villains and fun villains.