Kyrt wrote:
maybe it's the infantry that are wrong

As I see it :
Adeptus Titanicus started somewhere around 1:500 (by scaling the buildings.)
SM1/2 tried to go with 1:300 as it was as small as was possible in plastic infantry (6mm to top of head) and just about worked with the previously released titans. They did mk 1 rhinos/LRs etc to match. Even then however they fudged the vertical scale relative to the horizontal in order to make them slightly taller and look right unbased alongside based infantry.
This continued through most of SM2. Titans and fliers stayed at 1:500ish.
Even this fudge proved impractical (ever seen an original intact SM1 eldar guardian stand

?) and the range creeped up to around 1:250 for E40k inf (6mm to eyes.) Towards the end of the plastics era (nids and plastic chaos) they pushed the details even further and the infantry increased to 7/8/9mm??
By the time EA appeared SG models were released in all kinds of scales. FW were at least consistent, producing armour in scale with the new bigger infantry which works out at approx 1/5th of 40k scale. All this is a bit academic as they are fantasy models which don't really make any sense compared to real world armour anyway (as can be seen when compared to real life tanks at 1:300 scale.)
As you say, its the infantry which stuffed it all up!
personally I don't really care between armies, but do try to get each army's infantry and AVs something like consistent. Titan sizes always pushed my credibility button when seen in the artwork, so I tend to like to think of them at the size they are. I prefer to keep lighers small simply for practicality on flying stands.